BULLETIN OF THE FLORIDA STATE MUSEUM BIOLOGICAL SCIENCES Volume 13 Number I BREEDING BIRDS IN A FLORIDA SUBURB Glen E. Woolfenden and Sievert A. Rohwer * 1853 * UNIVERSITY OF FLORIDA Gainesville 1969 Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM are pub- lished at irregular intervals. Volumes contain about 300 pages and are not necessarily completed in any one calendar year. WALTER AUFFENBERG, Managing Editor OLIVER L. AUSTIN, JR., Editor Consultants for this issue: JEAN W. GRABER RICHARD R. GRABER HAROLD MAYFIELD Communications concerning purchase or exchange of the publication and all manuscripts should be addressed to the Managing Editor of the Bulletin, Florida State Museum, Seagle Building, Gainesville, FloridS 32601. Published February 10, 1969 Price for this issue $1.20 BREEDING BIRDS IN A FLORIDA SUBURB GLEN E. WOOLFENDEN AND SIEVERT A. ROHWERl SYNOPSIS: A study of bird populations in the residential suburbs of St. Peters- burg and Gulfport, Pinellas County, Florida based on observations made in three study plots totaling 100.5 acres during portions of two years, 1968 and 1964. The dominant vegetation is described in detail. Part I includes our estimates of the total number of breeding pairs for each plot, which varied from 200 pairs per 100 acres in new residential suburbs to 500 and 600 pairs per 100 acres in mature suburbs. Of the 11 species that breed in the three plots, four, the House Sparrow, Mourning Dove, Blue Jay, and Mockingbird, were the most abundant and accounted for more than 90 per cent of the total. House Sparrows alone comprised about 50 per cent of all breeding birds. Only four species not found in the quadrats, two of which are introduced, breed in similar habitats in the county. When natural area5 are replaced by suburbs a marked change in avian species composition occurs, and, with the eventual maturing of the suburbs, breeding populations increase in pairs per hundred acres from an estimated max- imum of 200 pairs to 500 or 600 pairs. Part I also discusses the birds breeding in peripheral habitats, total breeding populations for the two cities, non-breeding birds, and predators. Part II deals with the breeding biology of several of the more common breeders, excluding the .House Sparrow, - based on almost 900 nest records. A discussion of currently existing methods for measuring nesting success is followed by an explanation of a new method which may prove useful in certain other studies. By this method a calculated number of hypothetical unfound failures are added to the sample of known nests to compensate for nests found after incubation or egg laying has begun. Using our method we found that nest success was approximately 40 per cent for Mourning Doves breeding in pine- dominated suburbs and 20 per cent for those breeding in oak-dominated suburbs. Based on the same method nest success for Mockingbirds was about 52 per cent in the two habitats combined. A method of expressing nest-site preference based on the relative abundance of plants and the distribution of nests is proposed also. Additional information on phenology of nesting, clutch size, and nest location is given in the species accounts. Information is especially extensive for the Mourning Dove where 625 nestings were analyzed. ~Glen E. Woolfenden is Associate Professor of Zoology at the University of South Florida, Tampa. Sievert A.. Rohwer, formerly an undergraduate at the same institution, is a graduate student at the University of Kansas, Lawrence. Manuscript received 18 April 1967. -Ed. Woolfenden, Glen E., and Sievert A. Rohwer, Breeding birds in a Florida suburb. Bull. Florida State Mus., vol. 18, No. 1, pp. 1-88. 2 BULLETIN FLORIDA STATE MUSEUM Vol, 18 TABLE OF CONTENTS INTRODUCTION ACKNOWLEDGEMENTS DESCRIPTIONS OF THE PLOTS VISITS PART I DENSITIES AND COMPOSITIONS - PROCEDURES SPECIES ACCOUNTS Breeding Birds House Sparrow Mourning Dove Blue Jay Mockingbird Cardinal Red-winged Blackbird and Common Grackle Yellow-shafted Flicker and Red-bellied Woodpecker Starling Purple Martin SPECIES NESTING IN SIMILAR HABITATS SPECIES NESTING IN PERIPHERAL HABITATS EFFECTS ON N~TURAL HABITATS TOTAL BREEDING BIRDS COMPARISON WITH OTHER RESIDENTIAL HABITATS COMPARISON WITH N~TURAL HABITATS LATE SUMMER AND WINTER POPULATIONS TRANSIENTS PREDATORS PART II BREEDING BIOLOGY PROCEDURES Sources of Error in Existing Procedures Customary Methods Exposure Method A New Method for Estimating Nesting Success A Method for Expressing Nest-site Preference ~PECIES AcCOUNTS Mourning Dove Blue Jay Mockingbird Cardinal Red-winged Blackbird Common Grackle SCIENTIFIC NAMES OF BIRDS MENTIONED IN THE TEXT LITERATURE CITED 1968 WOOILFENDEN/ROHWER: SUBURBAN BIRDS 8 INTRODUCTION With the rapid growth of human populations man-modified en- vironments are of increasing importance to wildlife. In North America a type of man-modified habitat undergoing a particularly rapid ex- pansion is the residential suburb. In 1963 and 1964 we studied the birds inhabitating the suburbs of Pinellas County, Florida, which support a markedly large and rapidly growing human population. The immediate practical value of the study is related to investi- gations of the ecology of arboviruses. The Tampa Bay area of Florida, including Pinellas County, had three outbreaks of human St. Louis encephalitis between 1959 and 1963. The last and major epidemic in 1962 was the second largest outbreak of urban St. Louis enceph- alitis in the United States. As a number of bird species are known to carry St. Louis and other types of arbovirus (Hammon et al., 1951; Chamberlain et al., 1957; Ranzenhofer et al., 1957; Stamm, 1966), a knowledge of those species found in close proximity to man is man- datory to understanding arbovirus ecology. This may be especially true for breeding species, as young birds that have not built up an immunity to viruses are more important as hosts than old birds. Little information on bird populations in residential areas is avail- able, particularly for the western hemisphere. The work of Graber and Graber ( 1963) is a notable exception. Grosvenor ( 1916), Whitaker ( 1916), and Pitelka ( 1942) have published brief reports of high bird densities existing in the vicinity of man's establishments, but these were studies of nest densities and not breeding-bird den- sities. Our objectives were to determine species composition, density, habitat preference, and duration of the nesting season for the birds of surburban Pinellas County. Data on clutch size, productivity, and nest location based on almost 900 nests are included; such informa- tion seems rather scarce for Florida birds. Changes in the land-bird populations of Pinellas peninsula, as evidenced comparing our data with those of the early chroniclers of Pinellas County birds ( Pangburn, 1919; Fargo, 1926; Bent and Copeland, 1927; and DuMont, 1931), are discussed, as are differences between the Florida populations and those of suburban Illinois ( Graber and Graber, 1963) and New York ( Simmers, 1965), and between the populations in residential and natural areas ( Udvardy, 1957). 4 BULLETIN FLORIDA STATE MUSEUM Vol. 18 ACKNOWLEDGEMENTS We gratefully acknowledge the support and encouragement given by James0. Bond, Director, and William L. Jennings, Biologist, =at .the Eneephalitis Re-search Center, Tampa. Only through their efforts were «we able to. bring thisproject to completion. We are indebted to Robert-M: Mengel, Marion AnneJenkinson and especially Oliver L. Au5tin, Jr. for--their editorial contributions,and Marion A#ne Jenkinson, Dennis M. Power, Gerald G. Robinson and J. E,Fernandez for assistance with certain of the mathematical procedures. We areindebted to John R. Paul who took the photographs, Olga Lakela who identifiedcertain of the exotic plants, and especially to- Mrs. Jean Thomas who typed anearly draft and the final manuscript. Finally we would like to acknowledgethe many families living in our study area who, with but rare exceptions, weremost coOperative. The field work was supported by grant no. AI-05504-62 from the NationalInstitute of Allergy and Infectious Diseases, National Institute of Health, U. S.Public Health Service, Department of Health, -Education and.Welfare, Bethesda,Maryland, awarded to the Encephalitis Research Center, Tafnpa, Florida.A Grant-in-Aid of Research from The Society of the Sigma Xi awarded toWoolfenden helped us complete the manuscript. DESCRIPTIONS OF THE PLOTS Three study plots totalling 100.5 acres and representing the three major types of residential vegetation associations .were chosen and given the names "oak," "pine," and "new" in reference to their. dom-inant vegetative features ( fig. 1 and 2). Two plots ( oak and new)were in the city of St. Petersburg, the third was in adjacent Gulfport; all were within 4 miles of each other. The boundaries of all three plots were the midlines of public streets or alleys. Standing vege- tation ( overstory and understory but not ground cover) was measured by counting the number of individuals of each plant species and estimating the amount of ground each covered. In the field the diameter of the vertical projection of above ground parts was mea- sured for each plant large enough to be a potential nest site; the total space each plant species covered was later calculated from these measurements. Little overlap between over and understory plants occurred, but where it did the areas of both plants were included. In the vegetation summaries the ground -covered-by each plant species - is presented as a percentage of the total standing vegetation of the plot. Ground cover in all three plots consisted mainly of a few var- ieties of lawn grasses; differences in ground cover are mentioned below. Plant names are from Kurz and Godfrey ( 1962) and Bailey et al. ( 1949). OAK PLOT. - Located in St. Petersburg, bounded by 46th Street and the alleys east of 49th Street, south of 9th Avenue North, and 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 5 north of 5th Avenue North, a rectangle 385.7 yards, by : 221.3 yards containing 17.6 acres (7.9 h). Two streets and one unpaved alley extended the length of the quadrat and were intersected perpendic- ularly by one street. Another street extended one-quarter of the way through the width of the plot. Streets occupied 8.0 per cent of the quadrat and unpaved alleys 3.0-per ceht. The 53 dwellingi in'-the plot and a few additional structures occupied 12.8 per cent of the area. Two lots were vacant and both were wooded. Standing vegetation covered 28.3 per cent of the quadrat. Oak trees, genus Quercus, were dominant. The number of individuals and percentages each contributed to the standing vegetation were: Number of Percentage of Species individuals standing vegetation Turkey oak C Quercus Zaeuis) 181 44.78 Laurel oak (Quercus hemisphaerica) 45 18.49 Citrus ( Citrus spp.) 92 6.17 Jacaranda (Jacaranda sp.) 22 6.12 Longleaf pine ( Pinus palustris) 21 4.84 , Live oak (Quercus virginiana) 7 3.77 Bluejack oak ( Quercus incana) 11 8.68 Sand-live oak ( Quercus geminata) 14 8.50 Cherry laurel ( Prunus carotiniana) 29 1.66 Silk oak (GreviHea robusta) 15 1.12 An additional 25 or more plant species formed the remaining 5.97 per cent of the standing vegetation, no one accounting for more than one per cent. These plants are listed below in order of decreas- ing percentage. The palms were common small to medium-sized trees for which areas were not calculated because of their small and sparce canopies. Bamboo ( at least two genera) Azalea ( several genera) Ligustrum and privet ( Ligustrum and Saw palmetto ( Serenoa repens) Forestiera) Water oak C Quercus nigra ) Australian brush-cherry (Euge,iia Red maple ( Acer rubrum) paniculata) Brazilian pepper (Schinus terebinihi- Southern magnolia ( Magnolia grandi- folius) flora ) Strawberry guava (Psidium cattle- Sand pine ( Pinus clausa) ranum) White mulberry ( Morus alba) American holly ( Itex opaca) Podocarpus ( Podocarpus sp.) Firethorn ( Pgracantha sp.) Punk tree ( Melateuca leucadendra) Kumquat ( FortuneHa sp.) Vitex ( Vitex trifolia) Crape-myrtle ( Lagerstroemia indica) Loquat ( Eriobotrya iaponica) Feather palms ( probably mostly False-cypress ( Chamaecyparis sp.) Phoenix canariensis) Avocado ( Pena sp.) Cabbage-palm ( Sabal palmetto) 6 BULLETIN FLORIDA STATE MUSEUM Vol. 18 Figure 1. Habitats in the pine plot in suburban Pinellas County, Florida. Upper.- A view looking into an empty lot near the middle of the plot, the center of density of breeding Mourning Doves . Lower.-A view down an alley in the plot. 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 7 *7 Figure 2 . Habitats in the oak and new plots . Upper.-A dense stand of turkey oaks on the house lots in the oak plot. Lower.-A view in the new plot show- ing its less dense standing vegetation and rather uniform new houses. The few remaining old longleaf pines indicate the original vegetation was pine flat- woods. 8 BULLETIN FLORIDA STATE MUSEUM Vol. 18 PINE PLOT. - Located in Gulfport, bounded by' Blst and Gray .Streets -and 7th and 13th Avenues South, a rectangle 333.7 yards by 658.0 yards containing 9 city blocks and 45.4 acres ( 18.4 h). Two streets and three alleys running north-south, intersected perpendic- ularly by two more streets lay within the quadrat. Streets occupied 9.3 per cent of the plot, alleys 2.6 per cent. The plot was- almost entirely residential with 163 dwellings and 8 empty lots; buildings occupied 9.4 per cent of the 45.4 acres. The standing vegetation, predominantly longleaf pine, covered 10.1 per cent of the plot. Plant species that accounted for more than one per cent of the standing vegetation are tabulated below. Certain of these abundant plants were grown as hedges. We did not count the number of individuals in these instances. None of the 25 addi- tional species that made up the remaining 5.97 per cent of the pine plot vegetation accounted for more than 0.8 per cent of the total; the plants listed for the oak plot include virtually all of these. Number of Percentage of Species individuals standing vegetation Longleaf pine 231 50.49 Australian-pine 75 + hedges 18.06 (Casuarina equisetifolia) Water and laurel oak 26 6.91 Citrus 142 5.68 Silk oak 59 4.12 Punk tree 169 + hedges 8.90 Sand-live oak 11 3.56 Brazilian pepper primarily hedges 2.28 Slash pine ( Pinus emottit) 4 1.44 Ligustrum and privet 70 + hedges 1.86 Vitex 26 + hedges 1.28 NEW PLOT.- Located in a recently developed suburb ( houses built since 1956), afforded a more uniform environment with much less standing vegetation than the other two plots. Bounded by Benson and 26th Streets and 38th and 41st Avenues North in St. Petersburg, the quadrat included 6 city blocks, measured 660 by 275 yards, and contained 37.5 acres (15.2 h). Paved streets occupied 10.9 per cent of the plot. No alleys were present; concrete driveways covered 1.8 per cent of the surface. Each block contained 16 house lots; only. one lot was vacant. The 95 houses occupied 8,5 per cent of the quadrat. The standing vegetation, although dominated by longleaf pines, covered only 1.4 per cent of the plot. The plant species accounting 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 9 for more than one per cent «of the. standing vegetation are. tabulated below. Eighteen additional species made up the remaining 5.24 per cent of the standing vegetation all but two of which are in the list of vegetation on the oak plot, Lawn grasses, primarily St. Augustine (Stenotaphrum secunda- tum), were the .dominant ground cover in all three plots. The pine plot, and particularly the oak plot because of its dense overstory, had many patches of bare ground or leaf litter. Such areas were essentially nonexistant in the new plot where lawns were more lush and unpaved alleys were absent. From 11 to 16 December 1962 much of Florida, including Pinellas County, was subjected to a severe freeze. St. Petersburg registered a low of 20° F on 13 December, and the temperature remained below Number of Percentage of Species individuals standing vegetation Longleaf pine 45 46.49 Citrus 88 12.05 Ligustrum and privet 68 + hedges 9.89 Silk oak 28 8.87 Jacaranda 2 8.18 Podocarpus 96 8.08 Live oak 10 2.82 Juniper 58 2.29 Punk tree 47 2.10 Miscellaneous shrubs 42 1.85 Southern magnolia 9 1.74 Chinese tallow-tree ( Sapium 4 1.68 sebiferum) Turkey oak 1 1.12 Cherry laurel 4 1.12 Camphor-tree (Cinamomum 2 LOG camphora) Loquat 6 1.00 26° F for more than 7 hours ( Climatological Data, Florida, vol. 66, no. 12). The native trees that dominated our study plots showed no signs of damage, but other important species, particularly Australian- pine, punk, silk oak, Brazilian pepper, hibiscus (Hibiscus spp.), and ixora (Ixora coccinea), were severely injured. By spring many of the apparently dead shrubs and smaller trees had been cut to within a few feet of the ground. In most cases only the trunks and bases of the major limbs of the larger Australian-pines, punks, and silk oaks were living, and they also underwent severe trimming. For these 10 BULLETIN FLORIDA STATE MUSEUM Vol. 18 species, new growth from their trunks and the stubs of their major, · limbs produced bushy clumps of branchlets which did not resemble their normal arborescence. VISITS In 1963 we spent 582 man-hours in 105 visits to the plots. The totals for each were: oak plot, 44 visits, 180 man-hours; pine plot, 50 visits, 373 man-hours; and new plot, 11 visits, 29 man-hours. Censusing was begun during the fourth week in April and continued through December in the oak and pine plots, but ended on 11 July for the new plot. In the period between 21 April and 7 September we censused both the oak and pine plots an average of twice a week. Weekly visits continued through mid October and we also made one December census. Less tifne was spent censusing the new plot be- cause this habitat had relatively little vegetation and its bird den- sities were less than half those in the mature oak and pine plots. In 1964 we continued observations in portions of the oak and pine plots to establish the beginning of nesting, which we missed in 1963, and also to obtain additional nest records. In the oak plot 5.7 acres were chosen where the trees were densest. In the pine plot 10.2 acres ( two city blocks) in the south-central section were chosen for similar reasons. After an initial visit on 11 January, we censused the "restricted" oak and pine plots at least every week from 25 January through 27 September. In this season we made 39 visits totaling 95 man-hours to the oak plot and 40 vi5its totaling 195 man-hours to the pine plot. We tried to find all nests by searching all possible nest sites each week. Field maps were used to record new nests, fiedglings, adults caring for young, visiting species, migrants, and other pertinent in- formation. Data on the new nests were transferred to nest-record cards ( Woolfenden, 1965); cards for the active nests were taken in the Geld on succeeding trips to record the current status of each nest. In 1964 the use of a three-piece 15-foot pole with attachable mirror substantially increased the information gained on nest contents. PART I DENSITIES AND COMPOSITIONS PROCEDURES Biologists have been and continue to be plagued by the numerous sources of error inherent in the various practical methods of censusing animals. These sources of error have been well documented and, as 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 11 we have been unable to invent any better method, they need not be presented here. We do not believe the estimates biologists are ob- taining differ so much from the actual densities that censusing should be discontinued. On the contrary, we feel that employing a variety of the existing methods and using these as checks upon each other can produce a useful estimate of population sizes. Residential habitats are open and the birds living in them are accustomed to people. These two features made our census work somewhat easier. Of the several methods we used to establish the breeding-bird densities, four were particularly important: (1) plot- ting singing males, (2) plotting all nests built in one breeding season, ( 3) comparing total counts of adults taken on different days, and ( 4) calculating maximum number of active nests for one day. Plotting singing males, known nests, and other related information as developed by Williams ( 1936) is recommended by Kendeigh ( 1944) as the best means of establishing breeding-bird densities. Plotting singing males and territorial disputes on composite maps was useful in determining the densities of the highly territorial Mockingbirds, Cardinals, and Red-winged Blackbirds, but was of little value for House Sparrows, Blue Jays, and Mourning Doves. Composite mapping of all nests built during one breeding season is useful in determining the densities of strongly territorial species. Concurrently active nests usually belong to separate pairs, and chron- ological sequences of active nests in close proximity to each other were considered to represent the nestings of a single pair. Lines drawn around clusters of sequentially active nests fell within terri- torial boundaries as established by plotting the activities of the birds themselves and thus corroborated the results we obtained by the plotting of singing males. Total counts of adult birds made at intervals throughout the season gave useful density estimates for all species, and were of primary importance in establishing the numbers of the semicolonial Common Grackle and House Sparrow, and the Purple Martin and Blue Jay. House Sparrows tended to nest in colonies of 6 to 25 pairs. Estimates of the sizes of these groups soon became fairly consistent, and the total numbers of pairs was obtained by combining the num- bers found in these groups with the numbers of isolated pairs. Blue Jay territories are poorly defined and defended only against intruders showing particular behavior patterns ( Hardy, 1961); thus total counts give the best estimates of their densities. Following the dispersal of winter flocks, paired Blue Jays stay together almost 12 BULLETIN FLORIDA STATE MUSEUM Vol. 18 constantly, and densities can be established by counting pairs. Most lone adults were also scored as pairs; often they were known to have a mate on a nearby nest. The maximum number of nests active on one day of a breeding season establishes the minimum breeding density. To establish this daily maximum, each nest for which the age of the contents is known is extrapolated back to its date of beginning, and then the number of active nests is totaled for each day. Birds with territories partially out of a plot but nests within are balanced by those having nests out of a plot but territories partially within, provided (1) the plots are large and lie within a uniform habitat,(2) the species have small territories relative to plot size, and (3) the species confines its activ- ities to the habitat type. We agree with Hopkins and Odum ( 1953) who state that for Mourning Doves "the number of active nests can be used as a basis for estimating population density." We should add that extrapolating to the beginning of individual nest cycles and then using the maximum count for any one day makes the estimate even more accurate. Using the number of active nests for estimating breeding densities is par- ticularly good for Mourning Doves where little time elapses between successive nestings ( Swank, 1955). In other species, Blue Jays for example, weeks may be spent caring for fledglings ( Hardy, 1961), thus counts of active nests made while some pairs were caring for fledglings would result in underestimates. In most instances in the discussions that follow, including those cases using data from other authors, birds per unit area is presented as pairs per 100 acres for monogamous species and abbreviated such that 607 pairs per hundred acres will appear as 607p/100. SPECIES AccoUNTS BREEDING BIRDS Table I lists the densities of breeding birds in the three study areas in suburban Pinellas County in 1963: 11 species bred in the pine plot, 8 of the 11 bred in the oak plot, and 6 of the 11 bred in the new plot. Active nests were found in each plot for all species reported as breeding therein, and no other species was suspected to have bred in the plots. Our 1964 Beld work in restricted portions of the oak and pine plots added a nesting record for one species, the Great Crested Flycatcher whose status is discussed in the follow- ing section, "Species Nesting in Similar Habitats." 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 18 TABLE 1. BREEDING-BIRD DENSITIES IN THREE SUBURBAN HABITATS OF PINELLAS COUNTY, FLORIDA, IN 1968 IN NUMBERS OF PAIRS PER 100 ACRES. Pairs per 100 acres followed by actual Species number of pairs ( in parentheses), pine plot oak plot new plot 45.4 acres 17.6 acres 87.5 acres House Sparrow 830 (150) 217 (88) 127 (47) Mourning Dove 150 (68) 108 (18) 23 (8) Blue Jay 38 (15) 114 (20) 16 (6) Mockingbird 35 (16) 40 (7) 24 (9) Cardinal 18 (6) 29 (5) 8 (8) Red-winged Blackbird 11 (5) 5 (2) Red-bellied Woodpecker 5 (2) 11 (2) Common Grackle 18 (6) Purple Martin 18 (6) Starling 6 (1) 2 (1) 6 (1) Yellow-shafted Flicker 2 (1) Totals 607 (276) 526 (92) 203 (75) HousE SPARROW. - House Sparrows account for approximately half ( 55, 41, and 63 per cent in the pine, oak, and new plots, respectively) of all birds breeding in residential Pinellas County. Suburban areas provide an ideal habitat for the species as it requires grassy cover and open ground for feeding, dust-bathing, and gathering nest material, and human edifices or dense trees for nesting. Graber and Graber ( 1963) consider that in Illinois "residential areas are probably the most important habitat for the House Sparrow." In cities such as parts of Chicago and London where livestock numbers have de- clined, few House Sparrows now exist where formerly their popula- tions were high ( Rand, 1956; Fisher, 1954); as nesting sites are still available, reduced food sources are the limiting factor. Suburban areas contain few livestock ( our plots had none), but humans, both intentionally and unintentionally, and the vegetation, particularly lawn grasses, provide the necessary fare. The rapid spread of the suburbs augments House Sparrow populations, for in no other.present- day habitat are they so abundant. We recorded House Sparrow densities of 33Op/100 in the pine plot, 217p/100 in the oak plot, and 127p/100 in the new plot. The species nested in crevices in buildings in all three plots. In the new plot houses were rather uniform in construction with few crevices and, except for a few nest boxes, almost the entire population nested within covered roof vents. 14 BULLETIN FLORIDA STATE MUSEUM Vol. 18 The thick carpet of regularly mowed grass with few patches of bare ground may also have contributed to the relatively low density of sparrows in the new plot. Sparrows nested in trees only in the pine plot, where they built in the dense clumps of needles in the lower limbs of tall longleaf pines or in the dead tops of punk trees. The extensive areas of shade in the oak plot may have contributed to the lower densities there. That certain oaks provide suitable nest sites is substantiated by Rohwer's observation of nve House Sparrow nests in a copse of sand-live oaks in Winter Haven, Florida, in 1965. The sand-live oak has denser branches than the turkey oak, and its limbs end in numerous stout twigs capable of supporting nests. The factors common to the three different nest sites in trees appeared to be a relatively exposed location that also provided adequate support for the nest; in no case was the nest well shielded by leaves. Nesting in the dead tops of the punk trees killed by the freeze is of interest, as we have not observed nests in the foliated portions of punks. Few published studies of breeding densities of the House Sparrow are available for comparison. Hickey ( 1943) lists a census of 25 acres in a village in Alabama by M. T. Cooke, from which we calculate a density of 437p/100. Our average of 337p/100 is lower, but higher than the Grabers' (1963) 18lp/100 (range for three regions 136- 218p/100) on strip censuses in Illinois. MOURNING DOVE. - To support high nesting densities of Mourning Doves a habitat apparently must have trees suitable for nesting near a good source of nest material. Swank ( 1955) and Harris et al. ( 1963) point out the importance to Mourning Doves of open areas for gathering nest material, also for feeding and obtaining grit, which our own observations confirm. All nest material Cowan ( 1952) saw gathered came from within 20 yards of the nests; our own observa- tions extend this distance to 40 or 50 yards, which is still compara- tively short. In our residential plots doves gathered almost no nest material from mowed lawns, but took most of it from such bare spots as flower beds and the edges of driveways, streets, and alleys, as Swank ( 1955) also noted on a Texas college campus. Perhaps doves seldom search mowed lawns for nest material because the dense grass retards the rapid gait normally used when gathering it. The pine plot, or at least sections of it, appeared to be optimum dove nesting habitat, with its groves of spaced pines and ample open ground. The Mourning Dove generally prefers conifers for nesting ( Pearson and Moore, 1939; McClure, 1943; Quay, 1951; Harris et al., 1963), though in some regions it may not ( Boldt and Hendrickson, 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 15 1952). The lower density of doves in the oak plot may have resulted from the generally greater density of trees and the dominance of deciduous trees. In Georgia, Hopkins and Odum (-1953) found doves preferred edges to closed stands of forests. The starcity of both trees and bare ground accounts for the much lower density in the new plot. Table 2 lists breeding densities of Mourning Doves recorded in natural communities in southeastern United States and in man- modified habitats elsewhere. Dove densities in suburban Pinellas County are far greater than those in natural habitats in the south- TABLE 2. MOURNING DOVE BREEDING DENSITIES ( IN PAIRS PER 100 ACRES) IN VARIOUS HABITATS, NATURAL AND MAN-MODIFIED. Plot size State Habitat (acres) p/100 Source Georgia various 1000 8.3 Hopkins and Odum ( 1953) ( total of ten 100 acre plots) Georgia beech-magnolia 12.8 0 Norris ( 1951) hammock Georgia mature longleaf 48 0 Norris ( 1951) pine Georgia old field and 70 11.5 Norris ( 1951) fence row Florida longleaf pine- 25 8 AFN 12 (6) : census no. 15 turkey oak assoc. 25 12 AFN 13(6): census no. 14 Florida pine flatwoods 25 0 Robertson ( 1955) pine flatwoods 25 0 Robertson ( 1955) Minnesota city park 1957 160 40 Harris et al. ( 1968) city park 1958 160 58 Harris et al. ( 1968) city park 1959 160 61 Harris et al. ( 1968) Wisconsin park 5 100 Young ( 1949) Iowa town and farm 1938 220 118.6 McClure ( 1942) town and farm 1989 220 150.0 McClure ( 1942) Texas college campus, 81 1780 Swank ( 1955) 25% bldgs. & ( * 158 without added parking lots 14%, see Cowan, 1952: 519) Illinois residential areas 338 18 av. Graber and Graber ( 1968 ) ( strip census) - Florida residential areas 100.5 118 av. this paper; range 23 to 150 16 BULLETIN FLORIDA STATE MUSEUM Vol. 13 east, but are equalled by those in certain other man-modified en-: vironments. The abundance of the Mourning Dove as a breeding bird in suburban Pinellas County seems to be a recent development. Pang- burn (1919) and Bent and Copeland (1927) listed the species only as "a common bird in the central part of the county" and «a common resident in the open country on the mainland [east of Pinellas County]." Their comments show they did not ignore the birds of residential areas, where Pangburn ( 1919) considers the Mockingbird, Blue Jay, and Loggerhead Shrike, in that order, the most abundant birds; he calls the Mockingbird "the most conspicuous, most abundant and best known land bird in the county. Every yard has one or " I.more nests. Blue Jays he records as everywhere and in the city nest in trees along the streets and in the yards." Bent and Copeland ( 1927) call the Mockingbird "abundant everywhere about human habitations" and the jay "a common resident in towns." The present-day dense breeding populations of the Mourning Doves are not restricted to the 100.5 acres we happened to choose for study. On more than 100 miles of strip censuses taken in Braden- ton, Tampa, Clearwater, and St. Petersburg in 1962 and 1963 ( Wool- fenden and Rohwer, in press) the Mourning Dove was the fourth most. abundant species, exceeded only by the House Sparrow, Blue Jay, and Mockingbird. In Clearwater and St. Petersburg, the two cities in Pinellas County, the Mourning Dove was surpassed only by the House Sparrow. Had this species been as conspicuous a part of the suburban avifauna four decades ago, it surely would not have gone without comment by Pangburn or Bent and Copeland. The Grabers ( 1963) suggest the Mourning Dove may be adapting to the expanding residential habitat in Illinois. In 1907-1909 Forbes and Gross recorded 0.9p/100 in urban and rural residential Illinois; in 1957-1958 the Grabers obtained densities of 14.3p/100. If indeed Mourning Doves became an integral part of the subur- ban avifauna in Illinois and parts of Florida only during the past -40 years-·or·so, -the- phenomenon -warrants .further comment. -As resi- dential areas have always provided the proper nesting habitat, the change may have been toward an increased tolerance of man. In 1921 Nice ( 1923) noted on an Oklahoma college campus, that ap- proximately one-third of 76 doves left their nests when observers merely walked beneath the tree. At no time did a dove in our plots leave a nest containing eggs or young before the tree was being climbed, and frequently the bird had to be prodded to make it move. 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 17 The rapid turnover rate of dove populations ( Harris et al., 1963) could encourage the rapid acquisition of such a behavioral adaptation. Doubtless another important factor is the current prohibition of hunting in suburban afeas. Also noteworthy in connection with the increase in Mourning Doves is the apparent decrease in the numbers of Ground Doves in suburban Pinellas County in the last 40 years. Of the Ground Dove Pangburn ( 1919) writes "In St. Petersburg they are often seen about the door yards," and Bent and Copeland ( 1927 ) consider the species "A very common resident seen almost everywhere, but especially near houses. Today Ground Doves are decidedly uncommon in most Pinellas residential areas. On 37.2 miles of suburban habitat strip censusing in the county ( 25.5 miles in St. Petersburg, 11.7 miles in Clearwater) from July through October 1963 and 1964, we saw three Ground Doves, and on 184 trips to the three study plots, we saw only three Ground Doves, all in the pine plot. As an exception, in a suburb south of Largo that has numerous citrus trees and thick lawns but no tall trees, we heard six Ground Doves and saw three others on 23 May 1965. Thus the species was and .still is common in ·certain residential habitats. BLUE JAY. - Jay populations in Florida have probably increased with the development of residential suburbs. Breeding densities of the Blue Jay in forested regions are not high; the average for 50 censuses ( vols. 14-17) in Audubon Field Notes ( AFN in subsequent citations and literature cited) that record the species is 8.5p/100. In Georgia Norris ( 1951) found comparable densities of 11.7p/100 in a beech-magnolia hammock, 11.Bp/100 in mature longleaf pineland, and 4.3p/100 in old field and fence-row habitat. For southern Florida Robertson ( 1955) found 4p/100 in each of two pine flatwoods tracts and 6p/100 in forest edge. The Blue Jay was recorded as breeding only once ( 4p/ 100) in 5 years in a longleaf pine-turkey oak association in north central Florida ( AFN, 12-16). The highest density re- corded from 1960 through 1963 in AFN is 38p/100 ( Shugart, AFN, 15) in a small plot of 16 acres with considerable edge and near a subdivision. Kendeigh ( 1944) considers the Blue Jay a forest-edge species, in support of which he notes its steady increase over a 7-year period as an elm tree disease opened up the interior of a forest ( Kendeigh, AFN, 13). Suburban areas with trees resemble forest edge and provide good jay nesting habitat. The oak plot, with 28.3 per cent standing 18 BULLETIN FLORIDA STATE MUSEUM Vol. 13 vegetation, had a Blue Jay breeding density of 114p/100, far greater than any we have found in the literature. As the surrounding suburbs had similar vegetation, this high density was not caused by edge habitat. Furthermore the jays nesting in the pine and oak plots seemed to restrict their movements during breeding to the plots. The pine plot, with one-third the standing vegetation ( 10.1 per cent) had one quarter the jay density, 33p/100. Standing vegetation covered only 1.4 per cent of the new plot, and here the Blue Jay density was only 16p/100. The great density of jays in the oak plot must in part have been the result of more trees, but an additional unanalyzed factor was the difference in the type of trees that dominated the pine and oak plots and the food these might supply. The Grabers ( 1963) suggest the ecology of the Blue Jay is changing. The species declined in all habitats censused both in 1907-1909 and 1957-1958 in Illinois except residential areas. Forests that supported the bulk of the population in 1907-1909, and which have increased in total area since then, show a decrease in jay den- sities from 16.6p/100 in 1907 to 3.3p/100 in 1958. Residential areas, to the contrary, show an increase from 6.Op/100 in 1907 to 8,9p/100 in 1958, and now support most of the state's Blue Jays. MOCKINGBIRD. - Little information on densities of breeding Mock- ingbirds is available. It is a species of disturbed regions, and most breeding-bird censuses are taken in uniform natural habitats. For Maryland Stewart and Robbins ( 1958) list various edge habitats in the vicinity of residential and agricultural lands as preferred and give densities of 15p/100 for a residential suburb and 2p/100 for a census in mixed agricultural land. Our densities ( 40p/100 in the oak plot, 3lp/100 in the pine plot, and 24p/100 in the new plot), and those of Stewart and Robbins indicate that surburbs with many shrubs, extensive lawns, and spaced trees provide ideal Mockingbird habitat. An adaptability to man himself, suggested by Beddall ( 1963), may also be involved. Plotting Mockingbird nests and territories on vegetation maps of the oak and pine plots shows clearly that the species prefers the less densely wooded portions. Territorial boundaries usually coincide with wooded sections, and no territories included the most heavily wooded places. In Illinois the Mockingbird is rare in suburbs; only one bird was recorded on 333 acres of strip censuses scattered throughout the state. Densities higher than 3p/100 were recorded only in orchards in southern Illinois. Herein 5.5p/100 were obtained in 1907, 11.5p/100 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 19 in 1909 and 6p/100 in 1957. An overall decline in Illinois Mocking- bird populations is suggested for the 50-year period. Udvardy's ( 1957 ) suggesti on that walls, houses, fences, and other man-made structures diminish territory size and thereby increase density is an untested idea that, if valid, could help account for the high densities we obtained in residential surburbs. CARDINAL. - In 4 years of .AFN censuses (vols. 14-17) in eastern North America, the Cardinal occurs on 72 with an average density of 27p/100 (range 3p/100 to 88p/100). Of our three quadrats only the oak plot had a comparable density ( 29p/100); densities in the pine ( 13p/100) and new ( Sp/100) plots were considerably lower. These differences are probably directly related to differences in vege- tational densities, especially in the number of low trees and shrubs suitable for nest sites. Such potential nest sites were twice as plenti- ful ( 3.7 per cent) in the oak plot as in the pine plot ( 1.9 per cent); they covered only 0.5 per cent of the new plot. Roberts ( AFN, 17) lists 5Op/100 for a planted pine tract with a low hardwood understory in Georgia. This supports our contention that the predominant overstory plant species is not a factor directly affecting Cardinal abundance. A pine-dominated suburb containing an equal amount of low dense vegetation suitable for nesting prob- ably would support a breeding population as high as that found in the oak plot. RED-WINGED BLACKBIRD AND COMMON GRACKLE. - The low den- sities in our plots and the semi-colonial breeding habits of the two icterids make density comparisons with other habitats and areas unprofitable. The polygynous Red-winged Blackbird nested in the pine ( 3 males and 5 ~females) and new ( 2 males, 3 or 4 females) plots with densities of 6.6 and 5.4 males/100. We cannot explain their absence from the oak plot, where one less densely wooded section appeared suitable for nesting. The species was recorded on only 5 of 83 trips to the plot, and several of these records were of a single subadult male. As with other icterids, Red-winged Blackbird populations have increased tremendously in recent years, apparently in response to man's modifications of the environment. The Grabers give higher population estimates for this species than any other in Illinois for the summer of 1958. They recorded the species in most agricultural habitats but not in residential areas. On 103 miles of strip censuses made in four Tampa Bay cities including two in Pinellas County in 1962 and 1963, we found Red-wings the seventh most abundant 20 BULLETIN FLORIDA STATE MUSEUM Vol. 18 bird. Thus the species is a significant part of the breeding avifauna in suburbs in central Florida but not in Illinois. The Common Grackle nested only in the pine plot, which con- tained a small colony ( 13p/100) in 1963 and 1964. The species regularly visited the new plot, but was recorded only 4 times in 83 visits to the oak plot. It is generally suspected that grackles prefer conifers for nesting, although the species regularly nests in broad- leafed trees elsewhere ( Peterson and Young, 1950; Sprunt, 1954; Stewart and Robbins, 1958). The Common Grackle breeds commonly in suburban areas in Illinois ( Graber and Graber, 1963). YELLOW-SHAFTED FLICKER AND RED-BELLIED WOODPECKER, - The extensive territories and the relatively small size of our plots made it difficult to determine densities of the two resident woodpeckers. Our estimates for the Yellow-shafted Flicker of 2 and 6p/160, and for the Red-bellied Woodpecker of 5 and 1lp/100, in the pine and oak plots respectively, appear similar to published densities. The density of fickers on 30 breeding-bird censuses on which they were recorded (AFN 16 and 17) ranged from 1.2 to 2lp/100 with an average of 7p/100. Stewart and Robbins ( 1958) cite a density of 3p/100 for both an edge and a forest habitat in Maryland, and the Grabers ( 1963) estimate 2.3p/100 in residential Illinois. Red-bellied Woodpeckers recorded on 22 censuses ( AFN 16 and 17) had densities ranging from 2 to 22.2p/100. Stewart and Robbins ( 1958) list den- sities for four forest habitats ranging from 5 to 19p/100. In southern Illinois 2.5p/100 occur in forest habitat ( Graber and Graber, 1963). -An interesting difference between the Illinois and Florida populations is that in Illinois the Red-bellied Woodpecker is not associated with man. The Grabers saw none in their censusing of 333 acres of resi- dential suburbs. In Florida the species nests commonly in many suburbs and is a regular visitor to feeding stations. That Illinois is on the periphery of the species' range and has a much denser Starling population may account in part for this difference. No recent change in habitat preference in Pinellas County is suspected, as Bent and Copdaid ( 1927) foun-d it to be the commonest woildp6cker -and note that it often nests near homes. STARLING. - Although we have not been able to find a record of the first occurrence of the Starling in Pinellas County, the species probably arrived in the late 1930's. Up to 1931 ( DuMont, 1931; Howell, 1932) the species appears to have been absent. The St. Petersburg Christmas Bird Count ( AFN, 9: 140-141) first reported Starlings in 1954 when 5 birds were seen, and have recorded the 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 21 species annually in generally increasing numbers ever since. Starlings first bred in Tampa in 1942 ( Nicholson, 1964). Because the Starling is primarily a bird of urban and suburban habitats, few estimates of breeding densities are available for com- parison. Simmers ( 1965) estimated 26p/100 in residential Ithaca, New York, and Graber and Graber ( 1963) record 60-9Op/100 in suburban Illinois. The lower densities in Pinellas County ( 2 and 6p/100 in the pine and oak plots respectively), perhaps reflect the species' recent arrival. The greater number of Starlings in the oak plot undoubtedly reHects the larger number of nest cavities. Starlings foraged in the new plot, but did not breed there. Two Starlings were seen competing with a Red-bellied Wood- pecker for a nest hole 30 feet up a silk oak in the pine plot 25 January 1964. The Starlings succeeded in driving away the woodpecker, and on 1 February were seen taking nesting material to the hole; the nesting was -successful. On- 24 March 1966 in adjacent Pasco County S. E. Swimmer watched a Starling toss to the ground singly with its bill four Yellow-shafted Flicker eggs from a nest cavity whose entrance was 18 inches above the ground in a citrus tree. Swimmer chased the Starling away and did not see it near the nest _. again. The Grabers (1963 ) suggest that Starlings have been impor- tant in reducing the Illinois flicker population. As Starlings increase - in numbers in Florida, they may reduce the suburban populations of all woodpeckers. PURPLE MARTIN. - Purple Martin nest boxes were present only in the pine plot, with two boxes in one yard. One of the two houses was occupied by six pairs of martins; the other was used at various times by House Sparrows and Starlings. Martins frequently flew through the oak and new plots. SPECIES NESTING IN SIMILAR HABITATS Five species for which we obtained no nest records during our 1963 plot censusing undoubtedly breed in small numbers in the - -suburbs on the ' Pinellas -peninsula; -the--Great -Crested -Flycatcher, Downy Woodpecker, Screech Owl, and the introduced Budgerigar and Ringed Turtle Dove. In 1964 Great Crested Flycatchers fledged young from a nest box in the restricted pine plot. The species was recorded regularly in the pine plot in 1963 and in the oak plot both seasons, but only the one pair bred. Downy Woodpeckers, including birds of the year, were seen on 22 BULLETIN FLORIDA STATE MUSEUM V61. 18 37 out of 83 trips ( 1963 and 1964) to the oak plot; their breeding territories probably included portions of the oak plot in both seasons, but no nest was located in the plot. We never recorded the Screech Owl in residential Pinellas County, but we have received reports from other observers, and we have a fledgling specimen ( G.E.W. 2821) from nearby Bellaire. The feral nesting of the Budgerigar in Pinellas County is a recent event that probably became pronounced in the late 1950's. We have seen adults entering excavations in cabbage palms and dead stubs of longleaf pines, and they breed in the numerous nest boxes regu- larly. At present the colonies, though large, are local and scattered, and are usually found near dwellings where flocks are kept in cap- tivity. A small population of Ringed Turtle Doves has existed in the Mirror Lake region of St. Petersburg since at least 1953 when first reported by S. A. Grimes ( Sprunt, 1954). These doves nest in an area vegetated by many huge live oaks, which is poor habitat for Mourning Doves. Woolfenden observed an adult on a nest in one of these oaks in September 1962. The largest total count of the species was made in the fall of 1965 by Herbert W. Kale ( pers. comm.) who estimated 150 individuals near Mirror Lake where people feed them regularly. Two Catbirds, presumably a pair, remained in the same small part of the oak plot until 25 April 1963 but disappeared thereafter; we have no evidence that the species currently breeds anywhere on the peninsula, although apparently it bred in Clearwater in earlier years ( Howell, 1932). SPECIEs NESTING IN PERIPHERAL HABITATS Our definition of residential habitat, or suburbs, is more restricted than that of other authors, and we intentionally selected plots that lacked parks, large estates, numerous vacant lots, farmland, roadside habitat, or business districts. On frequent visits to other parts of the county we noted 21 additional species in these peripheral habitats that we did not find breeding in the suburbs. As might be expected the list includes the most frequent visitors to our true residential plots. In the following list the figure in parenthesis after each species is the number of times each was recorded in 184 trips to the plots, and an asterisk preceding the name denotes a Pinellas County breed- ing record established by us in the 1960's ( by observation of either an adult on a nest or nonHying young). These peripheral species are: 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 28 °Bobwhite (4) "Red-headed Woodpecker ( 26) .White-eyed Vireo ( 10) *Killdeer (0) °Eastern Kingbird ( 2) *Black-whiskered Vireo (1) Rock Dove ( 84) Gray Kingbird ( 18) * Prairie Warbler ( 18) °Ground Dove (2) *Fish Crow (86) 'Yellowthroat ( I) *Barn Owl (0) 'Carolina Wren (0) Eastern Meadowlark (0) *Common Nighthawk (17)*Brown Thrasher (4) ' Boat-tailed Grackle ( 20) Chimney Swift (81) *Loggerhead Shrike (2) ®Rufous-sided Towhee (30 ) Of the 21 species found in peripheral habitats, the following four visited our study plots with dependent fledglings: Boat-tailed Grackle ( pine and new plots), Red-headed Woodpecker and Gray Kingbird ( pine plot), and Rufous-sided Towhee ( oak plot). The towhees probably nested in the dense shrubbery on an estate across a wide street from the oak plot. The Prairie Warblers and White-eyed Vireos recorded frequently in the oak plot were migrants or post-nesting wanderers, as of course were some of the individuals of the species listed above. The scar- city in the plots of three widespread and abundant peripheral species, Carolina Wren, Brown Thrasher, and Loggerhead Shrike, seems worthy of emphasis. EFFECTS ON NATURAL HABITATS The replacement of natural habitats by residential suburbs has altered considerably the species composition and total bird density of Pinellas peninsula. The topography of the peninsula indicates that pine flatwoods, oak ridges, and mangrove (Auicennia, Laguncularia, and Rhizophora) and wax myrtle (Myrica cerifera) shores were the dominant plant associations the suburbs replaced. Observations in remnants of these natural habitats, and reference to earlier publica- tions ( Pangburn, 1919; Fargo, 1926; Bent and Copeland, 1927; Du- Mont, 1931; and Howell, 1932) show that in addition to 19 of the 21 species in the peripheral habitats ( the Rock Dove and Chimney Swift are deleted as they breed peripherally in urban areas) at least 10 other species found in the natural habitats are eliminated by the spread of suburbs: Red-tailed Hawk, Red-shouldered Hawk, Bald Eagle, Yellow-billed Cuckoo, Chuck-will's-widow, Red-cockaded Woodpecker, Scrub Jay, Brown-headed Nuthatch, Pine Warbler, and Bachman's Sparrow. Some colonies of nesting water birds have no doubt also been eliminated from certain areas. Densities of the Yellow-shafted Flicker, Red-bellied Woodpecker, Downy Woodpecker, Great Crested Flycatcher, Common Grackle, and Cardinal probably have changed little with the replacement of native habitats by suburbs. None of these six appears to be more plentiful in the vestiges 24 BULLETIN FLORIDA STATE MUSEUM Vol. 18 of natural habitats in the county than in mature residential areas. Evaluation of the changes in total breeding birds with the spread of suburbs into natural areas is hampered by lack of local censuses of the natural habitats. Nevertheless the changes appear to be marked. We have derived an average density of 20Op/ 100 for the natural habitats of Pinellas peninsula from the following information: Norris ( 1951) lists 197p/100 in a 43 acre plot of mature longleaf pineland in southern Georgia. From this figure, 2lp/100 of Eastern Wood Peewees and 6p/100 of Yellow-throated Vireos that do n6t breed in central Florida are deleted, leaving 17lp/100. Robertson ( 1955) censused two south Florida pine Hatwoods that averaged 45p/100. Adding 7Op/100 of Bachman.'s Sparrows that breed in Pinellas County from Norris' count gives a hypothetical Ggure of 115p/100. The existing flatwoods in Pinellas County contain numerous vegetation- choked shallow ponds where' Red-winged Blackbirds commonly breed. Using the adjusted figures from Norris ( 17lp/100) and Robertson ( 115p/100), and adding some for Red-wings and other pond edge species, such as the Yellowthroat, we estimate a maximum.of 20Op/100 for the original pine flatwoods on the peninsula. Breeding densities f6r xeric oak ridges, the original habitat--of the oak plot, are generally low. The densities recorded for a 25-acre plot in Alachua County (AFN, 12-16) yield a 5-year average of only 84p/100, which is reduced to 77p/100 by deleting the Yellow-throated Vireo. The turkey oak ridges in the interior of Pinellas peninsula probably supported a comparable low density of less than 10Op/100. The more humid oak ecotones on the shores of Tampa Bay and the Gulf were dominated by live oaks and probably supported a density closer to that of the pine flatwoods. In 1964 a remnant of live oak ecotone on Pine Key ( now called Tierra Verde) contained numerous pairs of Black-whiskered Vireos, Prairie Warblers, Cardinals, Rufous- sided Towhees, White-eyed Vireos, and Carolina Wrens (listed in order of decreasing abundance). Of these, only the Cardinal occurred in the Alachua County turkey oak plot. Originally the shoreline habitat was mangrove-wax myrtle, most of which has been replaced by residential developments. We cannot assess total population changes in this ecotone because we have found no censuses of the original habitat. It probably takes shore develop- ments longer to become mature suburbs with high breeding-bird densities because waterfront properties are frequently built on sand 811 and initially lack large trees. 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 25 As the density for mature residential sections of Pinellas County, exemplified, ·by the pine and oak plots, is approximately 550p/100, the replacement of natural habitats by mature suburbs increases the breeding=bird population by approximately 175 per cent (20Op/100 to 55Op/100). -The succession begins with an almost complete. de- struction of the original habitat and elimination of the avifauna as the land is cleared. As new suburbs are established, the bird popu- lation increases to the estimated original density ( as indicated by 203p/100 in the new plot), but with a marked change in species composition. As the suburb matures, density increases to well over twice the original, and a few more species are added. Although quantitative data are few, Homes, et al. ( 1957) describes a similar successional sequence for suburban London. TOTAL BREEDING BIRDS The cities of St. Petersburg and Gulfport covered approximately 54.00 square miles of Pinellas peninsula in 1963. Study of 1965 aerial photographs of the county showed 18.00 square miles of the suburbs to be mature, typified by the pine and oak plots, and 12.25 square miles to be new residential habitat. The remainder was either periph- eral ( see page 22) or urban. Line transects through the mature suburbs showed approximately 50 per cent of them to be dominated by oaks. The new suburbs are built almost entirely in former pine flatwoods, and are typified by the new plot. With these figures it was possible to estimate the total number of breeding adults of the 11 species inhabiting the 30.25 square miles of residential suburbs in St. Petersburg and Gulfport. Doubling the number of pairs per acre ( from Table I), and multiplying by the number of acres occupied by each type of residential habitat yields the following numbers of breeding birds rounded to the nearest 100: House Sparrow, 83,000; Mourning Dove, 32,800; Blue Jay, 19,400; Mockingbird, 12,400; Cardinal, 6,100; Red-winged Blackbird, 2,100; Red-bellied Woodpecker, 1,800; Common Grackle, 1,500; Purple Martin, 1,500 ( an unreliable figure as their density is greatly affected by the number of martin houses); Starling, 900; and Yellow-shafted Flicker, 900. The total for the 11 species is 162,400 adult individuals. Including the birds breeding in the 20 square miles of peripheral habitat within the city limits would augment this number significantly. Futhermore the production of young by the adults and the influx of wintering species and transients would more than double the number of birds present at certain seasons. 26 BULLETIN FLORIDA STATE MUSEUM Vol. 18 The 30.25 square miles now occupied by residential suburbs originally contained approximately 77,400 hreeding adults ( calculated by doubling our estimate of 2 pairs per acre and multiplying by the total acreage). Thus the total number of breeding birds has already increased by 84,900 individuals and as the suburbs mature, should increase by another 31,400 birds to reach a total of 193,800. This figure will continue to enlarge as the suburbs spread. COMPARISON WITH OTHER RESIDENTIAL HABITATS A number of censuses of man-modified environments are on record ( Cooke, 1923; Goodman, 1940; Steinbacher, 1942; and. Young, 1949) giving densities from 545 to 185Op/100, but we know of only two extensive surveys of birds breeding in residential suburbs: Simmers ( 1965) censused a 38-acre plot in Ithaca, New York for one season and Graber and Graber ( 1963) strip-censused 333 acres of residential habitat in Illinois. The available censuses indicate that mature north temperate suburbs typically support 15 to 30 species. Simmers lists 19 breeders for his plot and the Grabers list 28 potential breeders for suburban Illinois. Fitter ( in Homes, et al., 1957) lists 22 species known to have bred in the suburbs of London in 1936, of which 6 bred only in a 6-acre garden, leaving 16 species that bred in the residential suburbs. We recorded 16 species breeding in the residential suburbs of Pinellas County. The species inhabiting Florida suburbs differ considerably from those in New York and Illinois suburbs. The differences reflect the breeding ranges of the species involved rather than changes in the ecology between the northern and southern habitats. The breeding ranges of 9 of the species listed for New York and 10 of those listed for Illinois do not include central Florida; 9 of the 16 species breeding in suburban Pinellas County occur on Simmer's list and 11 occur on the Grabers' list; 8 species are common to all three areas and these account for 50.4 per cent of the Ithaca birds, 70.2 per cent of the Illinois birds and 89.1 per cent of the Pinellas birds. Two species amounting to 5.0 per cent of the Ithaca population and six species amounting to 8.5 per cent of the Illinois population we included in our category of peripheral species. Five of our 16 species do not appear on either Simmer's or Grabers' lists. Two of these, the Ringed Turtle Dove and the Budgerigar, are recent introductions and one, the Screech Owl, was probably over- looked in New York and Illinois. The absence of the remaining two, 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 27 the Red-winged Blackbird and the Red-bellied Woodpecker, seems to indicate different ecological preferences between the Pinellas and the northern populations. The Red-wing breeds commonly in all three states, and the Red-bellied Woodpecker is common in Illinois and Florida, but apparently neither species breeds in the northern suburbs. Mature residential areas of North America appear t6 have breed- ing-bird densities of 350-60Op/100. Simmers obtained a density of approximately 363p/100 in a maple-dominated suburb, which in- cluded 66p/100 of two semi-colonial forms. For Illinois the Grabers give an average of 434p/100. We found 526p/100 in the oak plot and 607p/100 in the pine plot. The House Sparrow is by far the most abundant suburban bird in all three states. The species made up 26 per cent of the birds breeding in the New York plot, 34 to 47 per cent of all summer birds in suburban Illinois, and 42 to 63 per cent of the birds breeding in our Florida plots. Additionally, 45 per cent of the birds we counted on 28.8 miles ( 17.1 in St. Petersburg, 11.7 in Clearwater) of strip cen- susing in Pinellas County suburbs were House Sparrows. In New York and Illinois the Robin and Starling were the next important species. Starlings, which have only recently invaded Pinellas County, are increasing in density. Robins do not breed in peninsular Florida, and their suburban niche seems occupied by Mockingbirds; both species feed on terrestrial invertebrates, and we observed a number of interspecific conflicts between territorial Mockingbirds and winter- ing or migrant Robins. COMPARISON WITH NATURAL HABrrATS When assessing bird densities in a variety of habitats it is best to compare study areas that are geographically near each other. Unfortunately few breeding-bird censuses are available for Florida. Robertson ( 1955) gives data for six natural areas in extreme southern Florida where he found forest edge habitat to have the greatest density ( 102p/100). Data from three other central Florida woodland habitats we have analyzed ( Rohwer and Woolfenden, 1969) show an oak-palm hammock 35 miles northeast of St. Petersburg to have the greatest density ( 183p/100), surpassing a mixed oak ridge ( 154p/ 100) and a maple-dominated wet woods ( 11lp/100) both some 10 miles north of our suburban plots. These low densities in the natural habitats of peninsular Florida make the high densities of birds breeding in the suburbs of the peninsula even more remarkable. 28 BULLETIN FLORIDA STATE MUSEUM Vol. 18 The. average. breeding-bird density in mature suburbs appears -- to be unsurpassed by any of the major natural habitats of N6rth America. Suburban densities are comparable to those found in flood- plain deciduous forest, northern coniferous forest, mixed deciduous forest, and edge habitat, which are the natural habitats with the . greatest breeding-bird.. densities ( Udvardy, 1957). The densities Udvardy lists for tundra, grassland, marsh, brush and scrub, oak- hickory forest, beech-maple forest, and mixed coniferous-deciduous forest contain only about half the density found in mature suburbs. The number of species in residential habitats is slightly lower or about equal to the number in the forested habitats of North America, and at least twice the number typically found in open habitats. LATE SUMMER AND WINTER POPULATIONS Winter populations of birds are difficult to estimate because in- dividuals typically wander widely, often in sizable flocks; nonetheless, some of our observations on the birds wintering in suburban Pinellas County seem worth recording. Of the 16 breeding species 14 are permanent residents; only the Great Crested Flycatcher and Purple Martin leave after nesting; the martins return in February, the fly- catcher in April. Only small seasonal fluctuations occur in the numbers of the four most abundant species ( House Sparrow, Blue Jay, Mockingbird, and Mourning Dove ). A late-summer increment caused by fiedglings is evident for House Sparrows and to a lesser extent for Blue Jays, but not for Mockingbirds and Mourning Doves which drive their young away from the breeding grounds. Concen- trations of juvenile Mockingbirds and also jays produced in suburbs later moved to habitats unsuitable for nesting ( Kale and Jennings, 1966; Rohwer and Woolfenden, in press). Starlings and grackles tend- ed to move out of the plots, while numbers of Red-wings and flickers increased slightly. Of the species that bred in our plots, Mourning Doves fluctuated most in numbers, but these fluctuations seemed no greater in winter than they were in summer when many doves ap- parently left the suburbs between nesting. attempts. Three species of n6nbreeding birds, Myrtle Warblers, Palm War- blers, and Robins,·form a. significant part of winter bird populations in suburban Pinellas County. Three Other species, the Yellow-bellied Sapsucker, Black-and-White Warbler, and American Goldfinch, are regular winter residents in small numbers. Cedar Waxwings occa- 1968 WOOLFENDEN/.ROHWER: SUBURBAN BIRDS 29 sionally are present in large flocks,·but their erratic wanderings make their presence unpredictable'. In summary the winter bird populations in suburban Pinellas County are as large or s6mewhat larger than the breeding populations. Peak bird densities in the suburbs probably occur in early fall when the breeding species and their young, the early transients, and some wintering species are present concurrently. TRANSIENTS We include the following data on transient species because they " show significant differences between the plots as stopping-off places for migrants. On each trip we recorded all species seen in the plots ( not including birds seen high overhead) and frequently we estimated the number of individuals. Of the 75 species we identiBed, we recorded 51 in the pine plot, only 4 of which were not seen in the oak plot. Two of these four, Eastern Kingbird and Pine Warbler, nest nearby in open or pine- dominated communities, and of the remaining two, the Bank Swallow is an open-country bird, and the Solitary Vireo was recorded only once. The oak plot, with its numerous large turkey oaks, is one of the most attractive habitats for migrant land birds in the county. Here we saw 71 of the 75 species, including 24 not recorded in the other quadrats. Eighteen of these 24 were species that breed in deciduous or northern coniferous forests and winter in large numbers in the tropics: 11 warblers, 3 vireos, 2 thrushes, 1 oriole, and 1 grosbeak. The variety of migrants and number of individuals present in the oak plot was sometimes high: on 29 March 1964 between 0645 and 0900 hours, while concentrating on finding nests, we recorded 16 species of migrants in the 5.7 acre restricted oak plot, including 20 White-eyed Vireos and 15 Red-eyed Vireos; on 22 March 1964 we estimated 60 Palm Warblers and 15 Parula Warblers. Unlike the pine plot migrants which were "flighty" and frequently left the plot entirely when approached, the migrants in the oak plot appeared to be systematically foraging through the vegetation. Virtually no transients visited the new plot ( censused 19 times, 23 April to 11 July, 1963), but as the vegetation grows this situation will change. PREDATORS Fish Crows, Blue Jays, gray squirrels (Sciurus carolinensis), house 80 BULLETIN FLORIDA STATE MUSEUM Vol. 18 cats, dogs, humans, and perhaps owls were the only important potential predators of birds in the plots. Snakes, raccoons (Procyon lotor), striped skunks (Mephitis mephitis), and hawks were not pre- sent, although they occur locally in natural habitats. Fish Crows frequently visited our plots, and although we did not observe them robbing nests they probably did so. Their visits were most frequent in early morning when they passed through at tree- top level as they dispersed from their roosts; frequently they landed in the tall trees and almost always were mobbed by resident jays, Mockingbirds, Red-wings, grackles, or House Sparrows. Mr. E. A. Scott, a reliable observer who lives in the pine· plot, claims he has observed crows and jays take eggs or small young from dove nests in his yard on several occasions. Possibly the late breeding of Fish Crows is scheduled to coincide with nesting peaks of other species. Howell ( 1932) states that Fish Crows nest later than Common Crows in Florida and gives nesting dates ranging from 30 April to 20 May ( 4 nests with eggs). Fresh eggs of Common Crows are usually found in February and March, the dates ranging from 21 January to 3 April. We observed a Fish Crow sitting on a nest, apparently incubating, near St. Petersburg Beach, Pinellas County, 15 May 1963. Two incidents confirm Blue Jay predation. A housewife who lives in the pine plot watched a jay rob an exposed Red-wing nest in her yard of two of its three young; she told us "the jay pecked at their heads the way they open a nut," while she watched from a window a few feet away. We saw a jay harassing a dove on an exposed nest in the oak plot. The dove showed the wing-up aggressive posture and struck vigorously when the jay approached closely. The nest contents were not seen, but it probably contained eggs, as it was a complete but new nest; by our next visit it was empty and deserted. Gray squirrels, frequently cited as nest predators, were common in the pine and oak plots, but we saw no predation. We never noted active squirrel and bird nests in the same tree, and jays vigorously chased squirrels from their own nest trees. Domestic cats and dogs present in all three plots undoubtedly accounted for some bird mortality, though we observed no predation and we do not feel they had much effect on the bird populations. Excluding climatological factors humans, in most instances in- advertantly, probably account for the largest number of nest failures, particularly for species such as Mockingbirds and Cardinals that build low nests. Mockingbirds seem to desert their nests readily 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 81 while the clutch is being laid and early in incubation; our own activities appeared to have caused several failures. The attacks Red-wings make on human intruders probably occasionally results in the intentional destruction of their nests, and one Mockingbird nest was intentionally destroyed by a property Owner who did not want us entering his yard· Care of standing vegetation, such as shrubbery pruning and tree removal, destroyed a few nests. An unknown predator, perhaps an owl, took three adult doves from nests in the oak plot within one month. Each nest when next seen was flattened and contained only a few rump feathers from an adult dove. Adjacent to the pine plot in the tower of Stetson Law College was a nest of Barn Owls. Several hundred pellets were removed and are currently being analyzed. A precursory examination shows that, the owls fed on several species of birds common in residential areas, including Mourning Dove, Blue Jay, Mockingbird, Purple Martin, and Red-bellied Woodpecker. Other remains, however, suggest that these Barn Owls foraged over the golf course, salt marsh, and overgrown fills on the opposite side of the campus; we found no evidence of their presence in the pine plot. PART II BREEDING BIOLOGY The primary objective of our study was to determine bird densities in suburbs. This required the use of several census tech- niques and extensive field work. The frequent visits to the study plots ( an average of 2 per week for 6 months in 1963, and 1 per - week for 9 months in 1964) allowed us to accumulate records on 867 nests. For four species we obtained sufficient records to ana- lyze the duration of breeding season, number of broods per year, clutch size, nesting success, productivity, and nest location. Nest records were kept for all species found breeding in the suburban study areas except House Sparrows. This ubiquitous species nests in the outer limbs of tall pines and in crevices of houses. Checking nests so placed would have left insufficient time for work on the other species. The nest records used herein and others accumu- lated for Florida are at the University of South Florida where any biologist may consult them. PROCEDURES We developed two apparently new methods for the analysis of certain nesting data. One deals with the vexing problem of 32 BULLETIN FLORIDA STATE MUSEUM Vol. 13 measuring nesting success and the other with the problem of quan- tifying data. on nest-site preference. Before introducing these we - define some terms and discuss the shortcomings of the existing procedures for measuring nesting success. Throughout Part II the term "nesting success refers to any or all of the various specific measures of survival of nest contents, such as nest success and Redging success. Nest success' is defined - as the percentage of those nests receiving a full clutch of eggs that Hedge at least one young. It is given by the expression Sn = C Ne / (1)(-f- ~ 100 where N f is the number of nests fledging at least one young, and No is the number of nests receiving a complete clutch of eggs. In some cases it is instructive to include in this calculation nests in which at least one egg appeared. Here the equation is modified to s, = ~ff_ h| 100 (2)n Ne~ where N® is all nests in which at least one egg appeared. Fledging success is the percentage of eggs in complete clutches that produce fledglings. It may be expressed as /-Y f h S f = 1 < j 100 (3) \EC / where Yf is the number of young fledged, and E c is the number of eggs in all complete clutches. In this calculation when one wishes to count all eggs laid, including those appearing in nests that fail before the clutch is completed, the expression is written s 1 - (-3-f~ 100 (4) f \El f where E 1 is all eggs laid. For many of our nest histories we established by extrapolation the date the clutch was complbted or the date the first egg was laid. The date the clutch was completed we obtained by sub- tracting the age of the embryos in days from the date this age was established or, if young were seen, by subtracting their age plus the time required for incubation from the -date the young were aged. The location of many nests prevented our checking their 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 88 contents the day they were discovered, but we were able to estab- lish the ages of many of these on later visits. Establishing whether or not young fledge from a nest is often difficult. With many species it is virtually impossible to observe fiedging or to. find fledglings for a large sample of nests. For such species fledging must be established by arbitrary means such as - defining a time ( age) after which nestlings are assumed to have left the nest successfully. The time limit used in a particular study is best defined by the investigator on the basis of his estimate of the frequency of nest failures just before fledging and the fre- quency of visits to the nests. When using this method it is important to exclude all nests not observed within the established time limit. The inclusion of nests whose success is determined by observation of Bedged young may bias the results toward success. This is true because all nests whose fledglings were not seen, including those that failed late in their cycle, may be listed as of unknown fate, and thus excluded from the calculations. For Mockingbirds we counted as successful all nests, and only those nests, in which nestlings were seen within 3 days of their normal fledging time. For Mourning Doves success and failure could safely be determined by the presence or absence of fledglings because, in our plots at least, newly fledged doves virtually always stayed close to their nest. SOURCEE OF ERROR IN EXISTING PROCEDURES CUSTOMARY METHODS. - Ornithologists are becoming increasingly aware of the deficiencies in the customary methods of measuring nesting success ( Mayfield, 1961; Skutch, 1966). The major difA- culty is with the kinds of nest histories that can be used for such calculations. Ideally only nests found before egg laying begins should be used in equations 2 and 4 above, and only nests found before the clutch is completed should be used in equations 1 and 3. The use of nests found later in their cycle results in a bias toward success because these nests have existed for a period during which other unfound nests may have existed and failed; we refer to these hypothetical nests as unfound failures. Snow ( 1955) was con- cerned with this problem in his estimates of nest success for the Blackbird and Song Thrush. His results, as computed by equation 2, were 41 and 36 per cent respectively, but he carefully notes that these Bgures are slightly biased toward success because nests found after the first egg was laid but before the clutch was conn- 34 BULLETIN FLORIDA STATE MUSEUM Vol. 18 plete were included in his calculations. Nolan ( 1963) calculated fledging success by equation 4 for a sample of 170 nests of 11 open-nesting altricial species; his result was 17.6 per cent. Both of these figures are below those obtained by Nice ( 1957), who based her calculations on 7,788 nest histories of open-nesting, altricial species appearing in 35 studies. Nest success computed from these data by equation 2 was 49 per cent, and fledging success by equation 4 was 46 per cent. We have studied 17 of the 35 papers Nice used, and were surprised, and disappointed, to find that not one of the investigators described his procedures for selecting usable nest records. Because of these omissions, and because visits varied from daily to weekly in these studies, we must assume that some of the investigators included in their calculations histories of nests found after they contained more than ohe egg or even after the clutch was complete. Incorporation of such nest histories may result in a large bias toward success; thus the average success figures given by Nice may be considerably less accurate than implied by the impressive columns of data from which they were calculated. As Mayfield ( 1961) pointed out, in many studies it is impossible to find a large number of nests at the beginning of their cycles and follow them to completion. A practical, though arbitrary, way to avoid discarding all less-than-ideal nest histories is to set a time limit beyond which nests are not included. Setting a time limit does not allow one to obtain real percentages of nesting success, but it does make possible comparisons with other data treated in a similar fashion. Generally the degree of comparability and the accuracy of the estimations of success increase as the time interval beyond which nests are not included in calculations is shortened. We strongly urge all students to consider these important sources of error and to give details of their procedures when re- porting on nesting success. To emphasize further the importance of these points we include here the analysis of 222 dove nests ( see table 3) found in the restricted pine plot of 1964. Three methods of limiting the nest histories included in the calculation of nest success are considered and their biases toward either success or failure ( or both) are noted. Any or all of these methods may have been used in the 35 studies summarized by Nice ( 1957). In our calculations we use equation 2 because Mourning Doves begin incubation when the first egg is laid. It should be emphasized that disturbance 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 85 caused by the observer, which almost invariably alters the chances of success, is present in all of the following calculations. First we use only ' those nests found before the hatching of the last egg, as established by direct observation of contents, and whose fates were known. Under these limitations substituting from table 3 in equation 2 gives: / 13 \ "< -~ 100 - 29.5 per cent "nest success 44 TABLE 8. DOVE NESTS EXISTING IN THE 10.2 ACRE PLOT OF 1964. Number of Class nestsCategory · Division I: Successful nests 1 Found before hatching (eggs seen) 13 2 Found before hatching as determined by extrapolation from subsequent aging of 57 nestlings ( eggs not seen) 8 Found after hatching ( young seen when found) 6 4 Found immediately after fledging 8 sub-total - 79 Division II: Unsuccessful nests 5 Found before hatching ( eggs seen) 81 6 Found before hatching as determined by extrapolation from subsequent aging of 15 nestlings ( eggs not seen) 7 Found after hatching ( young seen when found) 1 8 Found and failed while being built ( before laying of eggs) 28 9 Found while containing eggs as assumed by extrapolation ( see text for explanation) 85 10 Found and failed before eggs were laid as assumed by extrapolation ( see text for explanation) 26 sub-total 186 11 Division III: Nests of unknown fate 7 total nests found 222 Division IV: Hypothetical unfound nests ( see "New Method" section) 12 Calculated from preceding classes 5,6, and 7 9.8 18 Calculated from preceding class 9 12.4 14 Calculated from preceding classes 8 and 10 78.2 Total nests ( found and unfound) 821.9 36 BULLETIN FLORIDA STATE MUSEUM Vol. 18 where N , is Cliss 1 and N e is, classes l and 5 of table 3. Use of these nests results in a bias toward success because nests dis- covered at any stage of incubation are included, including some that have survived a time during which other undiscovered nests failed. Furthermore, increased failure caused by the observer is an important factor because with doves it is necessary to Rush the adult from the nest to see the eggs. A way to enlarge the previous sample of nest histories to be ~ used in the estimations of nest success is to include those nests found before hatching as determined by extrapolation. Substituting in equation 2 from table 3 gives: /70 ') 1 - 1 100 - 60.3 per cent "nest success,~ 116 ~ where N f is classes 1 and 2, and N e is classes 1, 2, 5, and 6 of table 3. As in the preceding example the existence of unfound failures biases the result toward success. The inclusion of nests found before hatching as determined by extrapolation is also a bias toward success because nests whose contents were not seen, some of which may have failed while they contained eggs, could not be included by extrapolation as our extrapolations were based mostly on subsequent aging of young. In this particular example the bias toward apparent success is especially large because few of our dove nests failed after the eggs hatched. In comparison with the preceding example the bias toward failure is reduced by the inclusion of nests from which the adult was never flushed. If all of these nests had been checked early in their cycle, more of them probably would have failed because the effect of human disturbance is most acute at that time. A still larger sample is obtained by including all nests, no matter when found, if they were determined either by observation or extrapolation to have had contents while under observation. Substituting in equation 2 from table 3 gives: 79 h - 1 100 = 49.1 per cent "nest success,161 ) where N f is classes 1, 2, 3, and 4, and N e is classes 1, 2, 3, 4, 5, 6,7, and 9 in Table 3. All of the possible biases incorporated in this estimate of nest success have been mentioned above. The major one is the inclusion of nests found long after hatching, which 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 87 disregards other concurrent undiscovered nests that must have failed. In these three examples calculated nest success ranges from 30 to 60 per cent, yet each example represents a method of selecting nest histories that earlier workers may have used. It is unfortunate that our sample contains too few nests found before the elutch was completed to_ permit estimating nest success, solely..on. ideal nest histories. An estimate made by combining nearly ideal nest histories for the pine plots of 1963 and 1964 by equation 2 gives a nest success of 40.5 per cent. As the per cent success ( see Mourning Dove account further on) obtained by the new method proposed below is closely similar for each of the two years, we feel that nest success for the two years was essentially the same. Thus 40.5 should closely approximate the actual percentage of nest success in 1963, and is a good standard to which the results in the preceding examples may be compared. ExposuRE METHOD. - In calculating fledging success by the ex- posure method of Mayfield ( 1960) a daily probability of survival for nest contents is computed for each stage of the nest cycle, incubation, hatching, and nestling. The probability of survival through any stage of the nest cycle is established by exponential expansion of the daily probability of survival for that stage, the exponent being the normal duration of the stage. Hatching is considered instantaneous and has an exponent of one. These ex- pansions assume that the probability of survival is independent for each day within a stage. Again assuming independence, the probabilities for the survival of eggs through incubation, the sur- vival of the embryo through hatching, and the survival of young through the nestling stage are multiplied together to obtain the probability of an egg producing a fledgling. The result when multi- plied by 100 is comparable to the per cent fledging success obtained by equation 4. In calculating nest success by the exposure method, each day that a nest survives represents a nest-day of exposure for the stage of the nest cycle being considered. The number of exposure days and the number of nests lost are totaled for each stage of the nest cycle. Dividing the number of nests lost in a stage by the number of nest-days of exposure for that stage gives the daily probability of nest loss for that stage of the cycle. Subtracting this figure from one gives the daily probability of nest survival for the stage being considered. A shortcoming of the exposure method, and one which Mayfield 88 BULLETIN FLORIDA STATE MUSEUM Vol. 18 clearly notes, is that the daily loss rates during the incubation and nestling periods must be assumed to be constant. Unfortunately the validity of this assumption can be tested only with a large sample of nesting data, including the histories of many nests found before incubation began. Thus the exposure method will probably prove valid for some studies but not for others, and we urge in- vestigators to consider this fault carefully before adopting the pro- cedure. The magnitude of error possible can be shown in the sample of 222 dove nests already considered ( table 3). For the 222 dove nests found in the reduced pine plot of 1964 the exposure method gives a probability of 0.0612 for the Redging of individual eggs; supposedly this figure is equivalent to 6.12 per cent fledging success using only ideal nest histories in equation 4. Observation showed that approximately 150 young doves were fledged. To obtain 150 fledglings using the success rate calculated by the exposure method the number of eggs laid would have to have been 2,451, a number far beyond the seasonal capacity of the approximately 40 pairs of doves breeding in this 10-acre plot. This error results mainly from a. high incidence of nest loss just after egg laying. Also doves that fail early in the incubation period renest almost immediately ( Hanson and Kossack, 1963), and as we found most nests soon after they were built, our sample con- tains more nest histories of this type than any other. By the ex- posure method of expanding daily probabilities, this high loss rate early in incubation is applied to the entire incubation period, yield- ing much too low a figure for the probability of survival of eggs. In using Mayfield's exposure method care must be taken to avoid rounding error in the exponential expansion of daily prob- abilities of survival, When the ~ exponent is large, a considerable error can result if the original daily probability of survival is rounded to only a few figures before expansion. Our calculations were done to 10 place accuracy. An advantage of Mayfield's method is that small lots of data in- sufficient for individual analysis may be tabulated for future com- bination with other data. The value of small lots of data is limited by the difficulty of determining whether or not loss rates have been constant. Loss rates definitely were not constant for our Mourning Doves. Our data did not show conclusively the loss patterns for Blue Jays, Mockingbirds, and Cardinals, thus we give exposure sum- maries for these species in tables 11, 14, and 16. In these tables data on nest success are given for the periods of the nest cycle in 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 89 rows 2,4, and 6, and data on fledging success are given in rows 3, 5, and 7; data on nest success without division of nest histories into the three periods are given in row 1. A NEW METHOD FOR ESTIMATING NESTING SUCCESS The formulas for calculating nesting success (of which equations 1-4 are examples) may be used with less than ideal samples of nest histories if an estimated number of nests that failed before they were discovered ( the unfound failures) is added to the denominator. A simple computation allows one to determine this number of unfound failures; but it may be used only if the observer searches in a manner that insures an equal probability of finding nests destined to succeed or fail. For example, if exposed nests, which are easier to find than better concealed nests, fail more frequently than the better concealed nests, a larger per cent of nests destined to fail would be found per day than of nests destined to succeed, then discovery rates for the two classes are unequal and not comparable. An attempt to inspect all potential nest sites in a study area periodically is usually necessary to insure that nests destined to succeed or to fail are found at similar rates. As the standard error of a statistic ( such as an estimate of nesting success) decreases as sample size increases, confidence limits for an estimate of success narrow as the sample of nests increases. For any one sample size the standard error will vary some as the rates of nest loss and nest discovery vary; thus the standard error of an estimate of nesting success cannot be calculated readily. Without subjecting our data to computer analysis, it seems reason- able to assume that a fairly valid estimate of success is obtained if plotting the time in their cycle when successful nests are found ( to be explained) results in a fairly smooth curve. As more failures than successes are recorded in most studies, if the sample of successes is large enough, the sample of failures should be also. Our method for calculating the number of unfound failures is demonstrated in the following example: suppose that for a certain species 10 of 20 successful nests were found by day X of an average nest cycle. Suppose also that 5 other nests, found earlier in their cycle, failed on day X. One may predict that additional nests failed on day X that were not found because of their brief ex- istence. Assuming the rates of finding successes and failures are comparable, the number of these unfound failures would approxi- mate 5. Thus, on day X of the average nest cycle 10 nests failed, 40' BULLETIN FLORIDA STATE MUSEUM Vol. 18 5 found and 5 unfound. A similar estimate is made for each day ( or whatever time interval - is being used) of the normal nest cycle. The sum of these daily estimates gives the total number of unfound failures; adding these hypothetical nests to the de- nominator ( total number of nests) gives the best estimate of nesting success. The general statement for this method of calculatihg the number of unfound failures is given by the equation Fu = Ff .025 ). The index values for punk trees and silk oaks were undoubtedly higher in 1963 than they would be in normal years, as these trees were recovering from an unusually severe freeze of the previous winter and were much bushier than normal. Where vitex and podocarpus were both present our impression was that vitex was the preferred species, but podocarpus 74 BULLETIN FLORIDA STATE MUSEUM Vol. 13 showed a higher preference rating. This may be in part a function of the high density of the breeding population of Mockingbirds. If territorial boundaries were established by factors other than the presence and position of favored nest sites, there would be less choice of nest sites; rather, any suitable plant within the territory would have to be used. Podocarpus grew on more of the house lots than any other plant that Mockingbirds used for nesting and because of territorial location it sometimes offered the only nesting site available to a pair. TABLE 15. MOCKINGBIRD NEST-SITE PREFERENCE, PINE PLOT, 1963, Per cent of Per cent of Index Plant category vegetation nests value Punk 11.06 25.98 +2.8 Vitex (+) 8.65 18.52 +5.1 Podocarpus (+) 1.52 14.81 +9.7 Citrus 16.11 11.11 -1.5 Silk oak 11.68 7.41 -1.6 Juniper (+) 1,06 7.41 +7.0 Laurel oak 19.62 3.70 -5.8 Sand-live oak 10.11 3.70 -2.7 Ligustrum spp. 8.86 3.70 -1.0 Fig (+) 0.00 3.70 - Other plants* 21.82 0.00 -- The 11 plant categories covered 7,820 square yards; the sample size for nests was 27. Plants followed by (+) were lumped with "Other plants" for the G-test; nest distribution in these low plants departed significantly from random (p < .050 > .025 ). *All other standing vegetation in the plot except longleaf and slash pines and Australian-pine. In the oak plot 11 nests were distributed in 8 species of plants. This sample was too small for analysis, but it is worth noting that vitex appears to have been strongly favored as it contained three nests but represented only 0.3 per cent of the total vegetation. No Mock- ingbird nests were built in the predominant turkey oaks which tended to be tall trees lacking bushy limbs. Nest heights recorded for 61 Mockingbird nests ranged from 3 to 22 feet with a mean of 7.9 feet ( S.D. == 3.2 feet). Taylor ( 1965) also found a mean nest height of 7.9 feet for 151 nests in northern Louisiana. 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 75 CARDINAL We found 30 active Cardinal nests in the 2 seasons of censusing. The earliest nest, discovered 29 March 1964, presumably contained an egg on 21 March. The latest active nest failed 7 August 1963. Extrapolation from observed contents is based on a 13-day incubation period and a 10-day nestling period ( Laskey, 1944). As other active nests were discovered near the times of these extreme dates, apparent- ly nesting normally begins during the third quarter of March and ends in the first quarter of August. This provides ample time for the production of four broods, although more time would be needed for five. In Tennessee Laskey ( 1944) recorded a marked female that had 4 nestings, 3 of them successful, in each of 2 consecutive years, and Shaver and Roberts ( 1930) report a marked pair that raised 4 broods from 5 attempts in one season. These must be extreme cases. In our plots the average number of broods, based on records for the entire population, was much lower. Although the histogram of the 1963 breeding season (fig. 10) shows some indication of 3 peaks of nesting activity, we have no evidence of any pair Redging three broods. For the estimated 11 pairs of Cardinals that occupied the pine and oak plots in 1963, we recorded only 10 nests ( including one record based on observed fiedglings) that contained young more than 8 days old, and 2 of these were unsuccessful. It is improbable 10- N um be r of A ct iv e N es ts 5- 0 , C,"1",~~i~~ 1,1,11,11,1 ~--~-~ 11 Mar Apr May Jun July Aug Figure 10. Histogram of the numbers of active Cardinal nests per week for the pine and oak plots ( 63.0 acres) of 1963 combined. The hatched area repre- sents nests known by extrapolation to have been active before field work began. 76 BULLETIN FLORIDA STATE MUSEUM Vol. 18 that any .successful breeding occurred before field work began, for we found 6 nests late in their cycle shortly after we began censusing, and no recently fledged young. Thus in 1963 at least, the average number of successful broods per pair was considerably less than 2. The average clutch size for 18 nests checked during incubation was 2.56 eggs (8 clutches of 2 eggs and 10 of 3). This average may be low as we knew of three nests that lost one egg each and continued to be active. The mode for 93 nests from Tennessee ( Laskey, 1944), Oklahoma ( Nice, 1931), and Kansas ( Johnston, 1960) was 3 eggs, with 20 to 25 per cent of the nests containing 4 or rarely 5 eggs. The only mention of 2-egg clutches is by Ganier ( 1941), who states that near Nashville, Tennessee, "late summer nests often have but two eggs. Because of these data we caution those who might automati- cally exclude Cardinal nests with 2 eggs from their tabulations on clutch size. Nest success as estimated from nests found before the eggs hatched ( after equation 2) was 31.6 per cent ( 6 of 19 nests success- fully fledged at least 1 young). Because of our small sample of nests, we included in this calculation active nests for which success was based on an observation of fledglings; in cases where no fledglings were'found the nest was assumed to have failed. In this case this pro- cedure seems reasonable as recently fledged Cardinals remain near their nest and call frequently, and therefore are easy to find. We recorded the number of young in eight nests seen within the last 4 days of the nestling period. Assuming this number is the number of young that fledged, an average of 2.0 young left successful nests (2 nests fledged 3 young, 4 fledged 2, and 2 fledged 1). Further analysis of nesting success from our small sample of data for the Cardinal seems unwarranted. However, in order that these data might be added to those obtained by other workers, we have sum- marized them by the exposure method in table 16. The 33 Cardinal nests found in the pine and oak plots were located in 17 species of plants; as many of these plants constituted but small parts of the vegetation and contained only one nest, we have not analyzed nest-site preference for Cardinals. The only plant form that contained more than two Cardinal nests was citrus, which housed four nests in the pine plot and six in the oak plot. No nests ~ were found in longleaf pines or turkey oaks. The mean nest height for 38 nests was 7.9 feet ( S.D. = 3.3), with a range of 3 to 25 feet. The distribution was bimodal, with 6 nests 5 feet high and 6 nests 8 feet high; 14 nests were between 3 and 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 77 5 feet and 14 between 8 and 10 feet up. Shrub nesting accounted for the lower mode and tree nesting for the higher. The nests built in trees were in the lower limbs, but these were higher than the sites chosen in the shrubs. The mean is closer to the higher mode because of a few nests built high in trees. Taylor ( 1965) gives an average of 6.3 feet and a range of 3 to 24 feet for 39 nests in Louisiana. TABLE 16. CARDINAL NESTING SUCCESS DATA FOLLOWING MAYFIELD'S EXPOSURE METHOD.1 Row Category Exposure Loss 1 Entire nest period 188 nest days 18 nests ( incubation to Redging) Incubation 2 Complete nest 111 nest days 10 nests ( entire clutch) 8 Individual eggs 248.5 egg days 25 eggs ( including above) Hatching 4 Complete nest 7 nests 0 nests ( all contents) ( no time) 5 Individual eggs or young' 18 eggs 2 itemsi ( including above) (no time) Nestlings 6 Complete nest 84.5 nest days 3 nests ( all nestlings) 7 Individual nestlings 62 nestling days 6 nestlings ( including above) iNest histories from both years and all three plots are included. Whe number of eggs seen after clutch completion was used as the num- ber entering the hatching period; nests are included only if nestlings were seen within 4 days after hatching. Fledgling Cardinals soon moved to the upper regions of trees in our residential plots and were not seen in the low vegetation or on the ground until they were becoming independent. This may have been in response to the frequent ground-level disturbances that occur in residential suburbs, as in a nearby natural habitat small Cardinal fledglings tended to remain in the understory. 78 BULLETIN FLORIDA STATE MUSEUM Vol. 18 RED-WINGED BLACKBIRD We found 11 Red-wing nests in the pine plot and one in the new plot. Seven were built in citrus, from 6 to I2 feet from the ground three were built 4 to 5 feet high in vitex, and one was 8 feet up in a small stand of bamboo. The plant species that appear to be pre- ferred as nest sites locally in natural habitats, salt bush Baccharis halimifolia and wax myrtle, are rare in the suburbs. Clutch size was established for 6 nests: 3 had 2 eggs, 2 had 3 eggs, and one had 4 eggs. One egg each disappeared from a 2-egg, 3-egg, and the 4-egg nest; however, each successfully Redged young. COMMON GRACKLE The small colony of 6 pairs of Common Grackles nested high in the densest stand of longleaf pines in the pine plot. We were unable to climb to any of the 8 nests we found but one nest that blew down 22 March 1964 contained 5 nestlings of varying sizes. Nest building began during the second quarter in February 1964, and fledglings were seen from 22 March to 23 April. All breeding activity ceased by the second quarter of May. We obtained too few nesting data for the remaining five species that nested in our residential area study plots ( Yellow-shafted Flicker, Red-bellied Woodpecker, Purple Martin, Starling, House Sparrow) to warrant analysis. SCIENTIFIC NAMES OF BIRDS MENTIONED IN THE TEXT Red-tailed Hawk, Buteo Mmakensis Red-shouldered Hawk, Buteo Zineatus Bald Eagle, Haliaeetus Zeucocephalus Bobwhite, Colinus uirginianus Ring-necked Pheasant, Phasianus cotchicus Killdeer, Chamdrius vociferus Rock Dove, Columba livia Ringed Turtle Dove, Streptopetia risoria Mourning Dove, Zenaidura macroura Ground Dove, Columbigallina passerina Budgerigar, Metopsittacus undulatus Yellow-billed Cuckoo, Coccy:us americanus Barn Owl, T!/to atba Screech Owl, Otus asio Chuck-will's-widow, Cuprimulgus carolinensis Common Nighthawk, Chordeites minor Chimney Swift, Chaetura petagica Yellow-shafted Flicker, Colaptes auratus Red-bellied Woodpecker, Centurus carolinus 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 79 Red-headed Woodpecker, Metanerpes er!/throcephalus Yellow-bellied Sapsucker, Sphyrapicus uarius Downy Woodpecker, Dendrocopos pubescens Red-cockaded Woodpecker, Dendrocopos boreatia Eastern Kingbird, T!/rannus tyrannus Gray Kingbird, Tyrannus dominicensis Great Crested Flycatcher, M!/farchus crinitus Eastern Wood Pewee, Contopus virens Bank Swallow, Riparia riparia Purple Martin, Progne subis Blue Jay, Cyanocitta cristata Scrub Jay, Aphelocoma coerutescens Common Crow, Corous brachyrhynchos Fish Crow, Cori>us ossifragus Brown-headed Nuthatch, Sitta pusilla Carolina Wren, Thryothorus tudouicianus Mockingbird, Mimus poZYglottos Catbird, Dumetella carolinensis Brown Thrasher, Toxostoma rufum Blackbird, Turdus merula Song Thrush, Turdus phitometos Robin, Turdus migratorius Cedar Waxwing, Bombycilla cedrorum Loggerhead Shrike, Lanifts ludouicianus StarIing, Sturnus outgaris White-eyed Vireo, Vireo griseus Yellow-throated Vireo, Vireo flavifrona Solitary Vireo, Vireo solitarius Black-whiskered Vireo, Vireo akitoquus Red-eyed Vireo, Vireo otivaceus Black-and-white Warbler, Mniotitta uaria Parula Warbler, Paruta americana Myrtle Warbler, Dendroica coronata Pine WarbIer, Dendroica pinus Kirtland's Warbler, Dendroica kirtian,iii Prairie Warbler, Dendroica discolor Palm Warbler, Dendroica palmarum Yellowthroat, Geothlypis trichas House Sparrow, Passer domestious Eastern Meadowlark, Sturnetta magna Red-winged Blackbird, Agelaius phoeniceus Boat-tailed Grackle, Cassidix mexicanus Common Grackle, Quiscalus quiscula Cardinal, Richmondena cardinatis American Goldfinch, Spintm tristis Rufous-sided Towhee, Pipito erythrophthalmus Bachmans' Sparrow, Aimophila aestivalis Song Sparrow, Metospiza melodia 80 BULLETIN FLORIDA STATE MUSEUM Vol. 18 LITERATURE CITED AFN ( Audubon Field Notes). We make frequent reference to the.,annual breed- ing-bird censuses reported in this journal. Where we do no ·more Than sum- marize a series of censuses we give only AFN and the included v61ume numbers. Austin, 0. L., Jr. 1951. The Mourning Dove on Cape _God. Bird-Banding, 28: 149-174. Bailey, L. - H., et al. 1949. Manual of cultivated plants most -commonly grown in the continental United States and Canada. New York, The Macmillan Co. Beddall, B. G. 1968. Range expansion of the Cardinal and other birds in the north- eastern states. Wilson Bull., 75: 140-158. Bent, A. C. 1946. Life histories of North American jays, crows, and titmice. U. S. Natl. Mus., Bull. 191. ---1948. Life histories of North American nuthatches, wrens, thrashers and their allies. U. S. Natl. Mus., Bull. 195. Bent, A. C., and M, Copeland. 1927. Notes on Florida birds. Auk, 44: 371-386. Boldt, W., and G. O. Hendrickson, 1952. Mourning Dove production in North Dakota shelterbelts, 1950. J. Wildlife Mgmt., 16: 187-191. Burleigh, T. D. 1958. Georgia birds. Norman, University of Oklahoma Press. Chamberlain, R. W., R. E. Kissling, D. D. Stamm, and W. D. Sudia. 1957. Virus · of St. Louis encephalitis in three species of wild birds. Amer. J. Hyg., 65: 110-118. Cooke, M. T. 1923. Report on bird censuses in the United States, 1916 to 1920. U.S.D.A. Dept. Bull., 1165: 1-84. Cowan, J. B. 1952. Life history and productivity of a population of Western Mourning Doves in California. California Fish & Game, 38: 505-521. DuMont, P. A. 1981. Summary of bird notes from Pinellas County, Florida. Auk, 48: 246-255. Fargo, W. G. 1926. Notes on birds of Pinellas and Pasco Counties, Florida. Wilson Bull., 38: 140-155. Fisher, J. 1954. A history of birds. London, Hutchinson House. Ganier, A. F. 1941. Through the seasons with the Cardinal. Migrant, 12: 1-4. Goodman, W. 1940. Farm buildings and open woodland. Bird-Lore's Fourth Breeding-Bird Census. The Season, Supplement to Bird-Lore, Vol. 42. Goodwin, D. 1956. The significance of some behaviour patterns of pigeons. Bird Study, 8: 25-37. ---1963. Nodding, driving and caressing in pigeons. Ibis, 105: 268-266. Graber, R. R., and J. W. Graber. 1963. A comparative study of bird populations in Illinois, 1906-1909 and 1956-1958. Illinois Nat. Hist. Surv., 28 ( Art. 3): 888-528. Grosvenor, G. H. 1916. The world's record for density of bird population. Bird- Lore, 18: 77-84. _Hammon,-W. -MeD:, W, C, Reeves, and G. E, Sather. 1951. Western equine and St. Louis encephalitis viruses in the blood of experimentally infected wild birds and epidemiological implications of findings. J. Immunol.,67: 857-367. Hanson, H. C., and C. W. Kossack. 1968. The Mourning Dove in Illinois. Tech. Bull. No. 2, State of Illinois, Dept. of Cons. Hanson, W. R., and R. F. Labisky. 1964. Association of pheasants with vegeta- tive types in east-central Illinois, Trans. 29th N. Amer. Wildlife and Nat. Res. Conf., 29: 295-306. 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 81 Hardy, J. W. 1961. Studies in behavior and phylogeny of certain New World jays ( Garrulinae). Univ, Kansas Sci. Bull., 42 (2): 13-149. Harris, S. W., M. A. Morse, and W. H. Longley. 1963. Nesting and production of the Mourning Dove in Minnesota. Amer. Midl. Nat., 69: 150-172. Hickey, J· 1 1943. A guide to bird watching. New York, Oxford Univ. Press. Homes, R. C. ( chm.) et al, 1957. The birds of the London area since 1900. The New Naturalist, London, Collins. Hopkins, M. N., and E. P. Odum. 1958. Some aspects of the population ecology of breeding Mourning Doves in Georgia. J. Wildlife Mgmt., 17: 182-143. Howell, A, H. 1982. Florida bird life. New York, Coward-McCann Inc. Jackson, G. L., and T. S. Baskett. 1964. Perch-cooing and other aspects. of breed- ing behavior of Mourning Doves. J. Wildlife Mgmt., 28: 298-307. Johnston, R. F. 1960. Directory to the bird-life of Kansas. Univ, Kansas Mus. Nat. Hist. Misc. Publ. No. 28: 1-69. ---1964. The breeding birds of Kansas. Univ. Kansas Publ. Mus. Nat. Hist., 12: 575-655. Kale, H. W., II, and W. L. Jennings. 1966, Movements of immature Mocking- birds between swamp and residential areas of Pinellas County, Florida. Bird- Banding, 87: 118-120. Kendeigh, S. C. 1942. Analysis of losses in the nesting of birds. J. Wildlife Mgmt., 6: 19-26. ---1944. Measurement of bird populations. Ecol. Monogr., 14: 67-106. Kurz, H, and R, K. Godfrey. 1962. Trees of northern Florida. Gainesville, Univ. of Florida Press. Lack, D. 1954, The natural regulation of · animal numbers. Oxford, Clarendon Press. Laskey, A. R. 1944. A study of the Cardinal in Tennessee. Wilson Bull., 56: 27-44. ---1962. Breeding biology of Mockingbirds. Auk, 79: 596-606. Mayfield, H. 1960. The Kirkland's Warbler. Bull. 40, Cranbrook Inst. Sci. ---1961. Nesting success calculated from exposure. Wilson Bull., 73: 255-261. McClure, H. E. 1942. Mourning Dove production in southwestern Iowa. Auk, 59: 64-75. ---1948. Ecology and management of the Mourning Dove Zenaidura macroum ( Linn.) in Cass Co., Iowa. Iowa State College Agr. Exp. Sta. Res. Bull. 810: 855-415. ---1950. An eleven-year summary of Mourning Dove observations in the West, Trans. N. Amer. Wildlife Conf., 15: 835-348. Michener, J. R. 1951, Territorial behavior and age composition in a population of Mockingbirds at a feeding station. Condor, 53: 276-288. Nice, M. M. 1928. A study of the nesting of Mourning Doves. Auk, 40: 87-58. 1931. The birds of Oklahoma. Revised ed. Univ. of Oklahoma Biol. Surv. Publ. 8 No. 1. --1957. Nesting success in altricial birds. Auk, 74: 805-821. Nicholson, D. J. 1964. Earliest Starling ( Sturnus vulgaris) breeding record for Tampa. Florida Naturalist, 87: 91. Nolan, V., Jr. 1968. Reproductive success of birds in a deciduous scrub habi- tat. Ecology, 44: 305-818. 82 BULLETIN FLORIDA STATE MUSEUM Vol. 18 Norris, R. A. 1951. Distribution and populations of summer birds in south- western Georgia. Occ. Publ. No. 3 Georgia Ornith. Soc., Athens, The University of Georgia Press. Palmer, R. S. 1949. Maine birds. Bull. Mus. Comp. Zool., Vol. 102. Pangburn, C. H. 1919. A three months' list of the birds of Pinellas County, Florida. Auk, 86: 398-405. Pearson, A. M., and G. C. Moore. 1989, Nesting habits of the Mourning Dove in Alabama. Trans. N. Amen Wildlife Conf., 4: 468-473. Petersen, A., and H. Young. 1950. A nesting study of the Bronzed Grackle. Auk, 67: 466-476. Pitelka, F. A. 1942. High population of breeding birds within an artificial habitat. Condor, 44: 172-174. Putnam. L. S. 1949. The life history of the Cedar Waxwing. Wilson Bull., 61: 141-182. Quay, T, L. 1951. Mourning Dove studies in North Carolina. North Carolina Wildlife Res. Comm. Raleigh, N. C. Pp. 1-90. ---1954. Mourning Dove populations in North Carolina. North Carolina Wild- life Res. Comm., Raleigh, N. C. Pp. 1-47. Rand, A. L, 1956, Changes in English Sparrow population densities. Wilson Bull., 68: 69-70: Ranzenhofer, E. R., E. R. Alexander, L. D. Beadle, A. Bernstein, and R. C. Pickard. 1957. St. Louis encephalitis in Calvert City, Kentucky, 1955. Amer. J. Hyg: 65: 147-161. Robertson, W. B., Jr. 1955. An analysis of the breeding-bird populations of tropical Florida in relation to the vegetation. Unpublished Ph.D. dissertation, Urbana, Illinois, Univ, of Illinois. Rohwer, S. A., and G. E. Woolfenden. In press. Breeding-birds of two Florida woodlands: Comparisons with areas north of Florida. Condor. Shaver, J. M., and· M. B. Roberts. 1930. Sonic nesting habits of the Cardinal J. Tennessee Acad. Sci. 5: 157-170. Simmers, R. W. 1965. Residential area [breeding-bird census]. Audubon Field Notes, 19: 622-628, census no. 58. Skutch, A. F. 1966. A breeding-bird census and nesting success in Central America. Ibis, 108: 1-16. Snow, D. W. 1955. The breeding of Blackbird, Song Thrush and Mistie Thrush in Great Britain Part III. Nesting Success, Bird Study, 2: 169-178. Sokal, R. R., and F. J. Rohlf. 1968. Biometry. San Francisco, California, W. H. Freeman and Co. Sprunt, A., Jr. 1954. Florida bird life. New York, Coward-McCann Inc. Stamm, D. D. 1966. Relationships of birds and arboviruses, Auk, 83: 94-97. Steinbacher, G, 1942. Die Siedlungsdichte in der Parklandshaft. J. f. Orn,, 90: 342-859. Stewart, R. E., and C. S. Robbins. 1958. Birds of Maryland and the District of Columbia. N. Amen Fauna No. 62. Stone, W. 1937. Bird studies at Old Cape May. Vol. 2. Lancaster, PennsyI- vania, Intelligencer Printing Co. Swank, W. G. 1955. Nesting and production of the Mourning Dove in Texas. Ecology, 86: 495-505. 1968 WOOLFENDEN/ROHWER: SUBURBAN BIRDS 88 Taylor, W. K. 1965. Nesting heights of some Louisiana birds. Wilson Bull., 77: 146-150. Udvardy, M. D. F. 1957. An evaluation of quantitative studies of birds. Cold Spring Harbor Symposia on Quantitative Biology, 22: 801-811. Webb, J. W. ( ed.). 1967. Mourning Dove investigations 1948-1956, SE. Assoc. Game and Fish Comms., Tech. Bull..No, 1, ix + 166 pp. Whitaker, J. R. 1916. A record bird census. Bird-Lore, 13: 248-249. Williams, A, B. 1986. The composition and dynamics of a beech-maple climax community. Ecol. Monogr., 6: 317-408. Woolfenden, G. E. 1965. A nest-record program for Florida. The Florida Naturalist, 38: 22-28. Woolfenden, G. E., and S. A. Rohwer. In press. The relative abundance of bird populations in residential districts of the Tampa Bay area. Florida State Board of Health Monogr, No. 12. Young, H. 1949. A comparative study of nesting birds in a five-acre plot. Wilson Bull., 61: 36-47. Contributions to the BULLETIN OF THE FLORIDA STATE MUSEUM may be in any field of biology. Manuscripts dealing with natural history or systematic problems involving the southeastern United States or the Caribbean area are solicited especially. Manuscripts should be of medium length-50 to 200 pages. Examination for suitability is made by an Editorial Board. The BULLETIN is distributed worldwide through institutional subscriptions and . exchanges only. It is considered the responsibility of the author to distribute his paper to all interested individuals. To aid in this, fifty copies are furnished the author without cost. PREPARATION OF MANUSCRIPT Highly recommended as a guide is the volume: Conference of Biological Editors, Committee on Form and Style. 1960. Style manual for biological journals. Amer. Inst. Biol. Sci., Washington. 92 p. Manuscripts should be typewritten with double spacing throughout, with ample margins, and on only one side of the paper. The author should keep a copy; the original and a carbon must be submitted. Tables and legends of figures should be typed on sheets separate from the text. Several legends or tables may be placed on a single sheet. Illustrations, including maps and photographs, should be referred to as "figures." All illustrations are reduced to a maximum of 4-1/4 by 7-1/8 inches. Size scales, wherever they are necessary, should be incorporated into the figure. References to literature should conform with the bibliographic style used in recent numbers of the BULLETIN. Spell out in full the titles of non-English serials and places of publication. Footnote material should be kept to a minimum. However, provide copy for a footnote detailing the title, affiliations, and address of the author (see recent numbers of the BULLETIN). Manuscripts must be accompanied by a synopsis-a brief and factual summary (not a mere description) of the contents and conclusions, which points out the presence of any new information and indicates its relevance. In it list all new organisms described and give their ranges; indicate all taxonomic changes pro- posed. The synopsis, written in full sentences, should be concise, but completely intelligible in itself without references to the paper, thereby enabling the busy reader to decide more surely than he can from the title alone whether the paper merits his reading. The synopsis will be published with the paper. It does not replace the usual conclusions or summary sections. It may also serve as copy for the abstracting services. Manuscripts and all editorial matters should be addressed to: Managing Editor of the BULLETIN Florida State Museum Seagle Building Gainesville, Florida