Nesting Biology of Mallards in West-central Illinois Aaron P. Yetter, Joshua D. Stafford, Christopher S. Hine, Matthew W. Bowyer, Stephen P. Havera, and Michelle M. Horath Illinois Natural History Survey Bulletin Volume 39, Article 1 September 2009 Institute of Natural Resource Sustainability Institute of Natural Resource Sustainability William Shilts, Executive Director Illinois Natural History Survey Brian D. Anderson, Director Forbes Natural History Building 1816 South Oak Street Champaign, Illinois 61820 217-333-6880 Citation: Yetter, A.P., J.D. Stafford, C.S. Hine, M.W. Bowyer, S.P. Havera, and M.M. Horath. 2009. Nesting biology of Mallards in west-central Illinois. Illinois Natural History Survey Bulletin 39(1):1–38. Science editor: Jeff Levengood Production editor: Charles Warwick US ISSN 0073-4918 US ISBN 1-882932-22-6 Printed by authority of the University of Illinois © 2009 P0276370—.45M—09-09 Printed with soy ink on recycled and recyclable paper. 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Missouri Department of Conservation 2206 W. St. Joseph Perryville, MO 63775 Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 Study Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Trapping and Transmitter Attachment . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Radio Telemetry and Nest Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Nesting Habitat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Recruitment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Statistical Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Nesting Parameters and Body Condition . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Hen, Brood, and Duckling Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Morphological Measurements and Body Condition Indices . . . . . . . . . . . .7 Nesting Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 Brood Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 Recruitment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Mass and Body Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Nest Initiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Nesting Attempts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17 Clutch Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 Egg Hatchability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 Renesting Effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 Nest Success. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19 Nesting Habitat Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19 Hen Success . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 Brood Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 Recruitment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 Conclusions and Management Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 ii Nesting Biology of Mallards in West-central IllinoisSeptember 2009 1 ABSTRACT The number of Mallards (Anas platyrhynchos) breeding in Illinois and eastern North America has increased in recent decades; however, few studies have investigated the nesting biology of Mal- lards outside primary production areas. Therefore, we radiomarked resident female Mallards (n = 148) in west-central Illinois during 1998–2003 to assess nesting parameters and evaluate recruit- ment. Mean initiation date for first nests ranged from 22 April to 6 May, and the majority (75%) of nests were initiated by 20 May. Therefore, the majority of nests were predicted to hatch by 24 June. The nesting season averaged 88 days (range: 77–103 days). The proportion of unsuccessful females that renested ranged from 50.0–85.7%, and adults were more likely to renest (75.0%) than yearlings (48.0%). Nest success ranged from 9.8–33.3% and was 19.6% overall; hen success was 28.3%. Initial brood size was 8.2 ± 0.3 ducklings, but brood size declined to 3.0 ± 0.6 ducklings by 17 days posthatch. Brood survival to 20 days was 0.759 ± 0.081, and 20-day duckling survival was 0.413 ± 0.035. Female survival during spring-summer ranged from 0.546–1.00 and averaged 0.710 ± 0.096. Likewise, estimated Mallard recruitment varied annually (range: 0.302–0.672 female ducklings/female). Assuming constant female and duckling survival, we estimated that a recruitment rate of 0.613 female ducklings/adult female was necessary to maintain a stable Mal- lard breeding population in west-central Illinois. Estimated Mallard reproduction and recruitment was similar to that observed in other areas of North America. Nest success and hen success approached or exceeded estimated thresholds for population stability in most years; however, hen success averaged over the study period was insufficient for local population maintenance and growth. Female survival was comparable to that observed in other studies but may have limited population growth in some years. Duckling survival was sufficient for population maintenance. Management designed to enhance hen success and brood habitat may augment Mallard recruitment in west-central Illinois. INTRODUCTION The Mallard (Anas platyrhynchos) is the most abundant duck in North America; thus, it is socially, economically, and ecologically impor- tant (USFWS 2007a). Further, the Mallard is the most frequently harvested duck in Illinois, the Mississippi Flyway, and the United States (USFWS 2007b). Consequently, Mallards have been the focus of intense scientific investigation in North America. Most previous studies of Mallard breeding ecology have been conducted in the north-central United States and central Canada (i.e., the Prairie Pothole and Parkland regions) with little attention given other areas. However, recent studies have investigated breeding ground demographic rates in Califor- nia, the Great Lakes Region, and eastern North America (Simpson et al. 2005, Hoekman et al. 2006a, 2006b, Chouinard and Arnold 2007, Coluccy et al. 2008, Davis 2008). Mallard breeding populations outside of the Prairie Pothole Region have expanded in recent years. In the late 1980s, an estimated 225,000 Mallards bred annually in Wisconsin, Michigan, and Ohio (Petrie 1999); this estimate increased to 503,000 in 2007 for Wisconsin and Michigan alone (USFWS 2007a). Wetlands in nontraditional nesting areas, such as the Great Lakes Region, are less susceptible to drought than prairie wetlands (Simpson et al. 2005), resulting in more stable nesting and brood- rearing conditions that may have contributed to this increase. Breeding Mallards were not abundant in Illinois during the early 1900s, although they may have been common in the glaciated pot- hole region of northeastern Illinois (i.e., Boone, Cook, DeKalb, DuPage, Kane, Lake, McHenry, Will, and Winnebago counties [Havera 1999]). Ford et al. (1934) classified Mallards as perma- nent residents of the urbanized Chicago region. Vol. 39 Art. 12 Illinois Natural History Survey Bulletin Prior to this, Kennicott (1855) observed that nesting Mallards were abundant in Cook County, and Nelson (1876:138) reported that Mallards commonly nested in Lake and Cook counties. Research conducted in 1942 in north- eastern Illinois documented low densities of Mallard nests (1.1 nest/km2; [J.B. Low, Illinois Natural History Survey (INHS), unpublished data]), but by 1956 Mallards were nesting in “substantial numbers” in northeastern Illinois (S.H. Garland, INHS, unpublished data). Ha- vera (1999:105–106) identified 15 records of nesting Mallards in 9 northern Illinois counties prior to 1930, but by 1990 Mallards were re- ported to nest in every county in Illinois. Em- phasizing this increase, Yetter (1992) observed 3.4 breeding pairs/km2 in northeastern Illinois during the early 1990s. The North American Breeding Bird Survey (BBS) indicated Mal- lards increased 214% in Illinois from 1966 to 1989 (Droege and Sauer 1990, Havera 1999), although recent data from the BBS indicated that Mallard population growth was leveling off (Sauer et al. 2007). Due to their expanded range, Mallards pro- duced in the Great Lakes states (including Il- linois) comprise an increasing proportion of the Mallard harvest in Illinois. For example, 9% of Mallards harvested in Illinois were produced in the Great Lakes states during 1961–1975, whereas 28% of the harvest originated from this region in the 1990s (Zuwerink 2001). Clearly, this increased harvest emphasizes the importance of the Great Lakes Region to Il- linois and mid-continent Mallard populations. However, little information existed regarding the productivity of Mallards along the Illinois River corridor, an important ecoregion to wa- terfowl. Therefore, we initiated this study to 1) determine nesting effort and success; 2) assess brood, duckling, and female survival; and 3) estimate recruitment of Mallards breeding in west-central Illinois. STUDY AREA We selected study areas based upon accessibil- ity and perceived resident Mallard densities. These included Banner Marsh State Fish and Wildlife Area (Banner) and the Prairie Plan site of the Metropolitan Water Reclamation District of Greater Chicago (MWRD) (Fig. 1). Banner was located in the Illinois River floodplain in Fulton and Peoria counties. This site was lev- eed from the Illinois River for agriculture and subsequently surface-mined for coal before its acquisition by the state of Illinois in the 1980s. It was managed by the Illinois Department of Natural Resources (IDNR) for outdoor recre- ation and fish and wildlife habitat and consisted of 1,766 ha of wetlands and deepwater habitats, upland forests, idle grasslands, cattle pastures, hayfields, old fields, and row crops (Photo 1). Upland nesting cover at Banner included smooth brome (Bromus inermis), switch grass (Panicum virgatum), fescue (Festuca sp.), forbs (e.g., goldenrod [Solidago spp.]), autumn olive (Elaeagnus umbellata), multiflora rose (Rosa multiflora), and willows (Salix spp.). We did not conduct research at Banner after 1998 because of our inability to capture an adequate sample of females at this site. Prairie Plan was located in Fulton County and consisted of 6,284 ha of reclaimed surface- mined lands (Photo 2; Patterson 1982). This area was managed as a disposal site for bio- solids that were spread over agricultural fields and incorporated into the soil. Major land categories at MWRD included idle grasslands, hayfields, cattle pastures, row crop and small grain agriculture, upland forests, and a variety of wetland and deepwater habitats ranging from large lakes created by strip-mining for coal to small ponds and marshes. Upland nesting cover at MWRD was dominated by smooth brome, meadow fescue, orchard grass (Dactylis glomerata), timothy (Phleum pratense), alfalfa (Medicago sativa), red clover (Trifolium prat- ense), goldenrod, multiflora rose, autumn olive, and willows. METHODS Trapping and Transmitter Attachment We used decoy traps to capture Mallards prior to nesting during the period 1998 to 2003 (Pho- to 3; Sharp and Lokemoen 1987, Ringelman 1990). We did not detect an age-related bias in Nesting Biology of Mallards in West-central IllinoisSeptember 2009 3 Photo 2. Aerial photo of the Prairie Plan site of the Met- ropolitan Water Reclamation District of Greater Chicago (MWRD) in Fulton County, Illinois, April 1998. Photo by Michelle M. Horath. Photo 1. Aerial photo of the Banner Marsh State Fish and Wildlife Area (Banner) in Fulton and Peoria counties, Illinois, April 1998. Photo by Michelle M. Horath. Figure 1. Location of study areas for Mallard (Anas platyrhynchos) nesting biology investigations in west-central Illinois, 1998–2003. Fulton Peoria Figure 1. Location of study areas for Mallard (Anas platyrhynchos) nesting biology investigations in west-central Illinois, 1998–2003. Vol. 39 Art. 14 Illinois Natural History Survey Bulletin the trapability of female Mallards. We began trapping in mid-March, after the peak of spring migration (Havera 1999). We weighed (± 10 g) and banded individuals with USFWS size 7A leg bands. Additionally, we recorded culmen length, bill width, tarsus length, and tarsus width (± 0.1 mm; Byers and Cary 1991), and wing chord length (± 1 mm; Carney 1992, Hine et al. 1996). We aged females as yearling (first breeding season) or adult (≥ second breeding season) following Krapu et al. (1979a). We radiomarked females using prong and suture radio transmitters (Photo 4; Mauser and Jarvis 1991, Pietz et al. 1995) equipped with 120-day batteries and 12-hr mortality switches. Trans- mitters weighed about 1% (12–13 g) of a fe- male’s body mass at capture and were attached under local anesthetic (lidocaine). Handling time was < 30 min, and we released females immediately after transmitter attachment. Capture, handling, and transmitter-attachment procedures were approved by the University of Illinois Institutional Animal Care and Use Committee (Protocol # 03012). Radio Telemetry and Nest Monitoring We considered females to be residents if they attempted to nest or remained on the study area during the nesting season. We located radio- marked females by triangulation twice daily (≥ 6 days/week) between 0600 and 1300 hrs using vehicle-mounted, null- array antenna systems and hand-held antennas and recorded daily locations on aerial photographs (White and Garrott 1990, Gloutney et al. 1993, Samuel and Fuller 1996). Females located in nesting cover for ≥ 2 consecutive locations were approached on foot with a hand-held antenna in an attempt to locate nests by triangula- tion without flushing the female (Paquette et al. 1997). We searched for nests while females were away from the nest site and verified nest fate (i.e., active, abandoned, destroyed, or hatched) if a female was located off her nest for ≥ 2 consecutive telemetry loca- tions (Klett et al. 1986, Paquette et al. 1997). We conservatively evaluated evidence from destroyed nest sites to identify nest predators (Smith 1982, Sovada et al. 1996, Hernandez et al. 1997, Sargeant et al. 1998). For nests located during laying we determined initiation date by backdating the number of eggs pres- ent from the date of nest discovery (assuming a laying interval of one egg per day and partial nest predation had not occurred). Otherwise, we assessed nest initiation date by candling eggs (Weller 1956) and subtracting the esti- mated incubation stage and number of eggs present from the day the nest was found (Klett et al. 1986, Paquette et al. 1997). When we failed to locate a nest prior to depredation, we estimated nest initiation from the female’s daily movements or the first day she was located at the nest site. We visited nests on the estimated 18th day of incubation to determine the incubated clutch size, assuming partial nest predation had not occurred. We determined egg hatchability from the presence of whole eggs and membranes at the nest site (Davis et al. 1998), defined a successful nest as hatching ≥ 1 egg (Klett et al. 1986), and defined hen success as the prob- ability of a female having a successful nest in Photo 3. Decoy trap used to capture Mallards (Anas platyrhynchos) in west- central Illinois, 1998–2003. Photo by Michelle M. Horath. Nesting Biology of Mallards in West-central IllinoisSeptember 2009 5 one or more nest attempts (Cowardin et al. 1985, Klett et al. 1986). We located females with broods daily until 20 days posthatch, and we attempted to count ducklings multiple times each week from distant vantage points to ascertain brood and duckling survival. Brood females were flushed daily in 1998 to verify brood size; however, we reduced brood monitoring intensity in subsequent years by flushing broods once per week. Nesting Habitat We estimated the composition of Mallard nesting habitats at MWRD by digitizing cover types within 12.57-ha random circular plots (n = 50 each in 2001 and 2002). Habitat delineations were verified in the field and digitized on 1998 aerial imagery using ArcView GIS 3.3. We assumed the distribution of nesting habitats mea- sured in 2001–2002 were representative of the study period because habitat composition within plots was similar between years. Recruitment We defined recruitment (R) as the number of female ducklings surviving to 20 days posthatch per nesting female in spring. We estimated re- cruitment according to Mauser and Jarvis (1994) as: (R = HGSd/2), where H = hen success, G = mean brood size at hatch, and Sd = duckling sur- vival to 20 days posthatch. We monitored duck- ling survival to 20 days because most duckling mortality occurs within this period (Orthmeyer and Ball 1990, Mauser et al. 1994a). This method as- sumed a 50:50 sex ratio of ducklings, hence division by 2 in the equation. We estimated the proportional change in population size (C) each spring following Mauser and Jarvis (1994): C = S(1+DR/Sb), where S was the annual adult female survival (0.520 ± 0.029; Smith and Reyn- olds 1992:312), D was the ratio of annual yearling survival (0.556 ± 0.049, Smith and Reynolds 1992:312) to adults, R was our estimate of re- cruitment, and Sb was our estimate of summer (i.e., breeding season) female survival (age classes combined). STATISTICAl ANAlYSES Nesting Parameters and Body Condition We defined nesting-season length as the interval (days) from the date the first egg was laid to the date the last nest hatched or was destroyed. We compared mean number of nest attempts per female, initiation dates for first nests, incubated clutch size, and female body condition indices (i.e., body mass [g]/ wing chord [mm]; Ringelman and Szymczak 1985, Hine et al. 1996) among years, between age classes, and their interaction using two- way analysis of variance (ANOVA). We used Tukey/Kramer means comparison tests when significant (P ≤ 0.05) main effects were de- tected (Proc GLM, SAS Institute, Inc., Cary, NC). Nonsignificant (P > 0.05) interactions were removed from models. We used simple linear regression to evaluate the relationship between nest initiation date and incubated clutch size (Proc REG, SAS Institute, Inc., Cary, NC), and we tested for annual differ- ences in brood size at hatch and male body Photo 4. Prong and suture radio transmitter used to investigate the pro- ductivity of female Mallards (Anas platyrhynchos) in west-central Illinois, 1998–2003. Photo by Paul F. White. Vol. 39 Art. 16 Illinois Natural History Survey Bulletin condition indices using one-way ANOVA and Tukey/Kramer post-hoc tests (SAS Institute, Inc., Cary, NC). We modeled apparent nest success (Klett et al. 1986) and hen success using an information- theoretic approach as a constant function (intercept only) and with respect to female age (AGE), year (YEAR), and nest initiation date (NESTINIT, nest success model only; Burnham and Anderson 2002, Dinsmore et al. 2002). We conducted modeling using the GLIMMIX procedure using METHOD=LAPLACE and specifying a binomial distribution and logit link function (SAS Institute, Inc., Cary, NC). Further, we accounted for dependence in suc- cess rates of females monitored for > 1 year via the RANDOM statement. We determined best approximating and competing models by outputting second-order Akaike’s Information Criterion (AICc; Burnham and Anderson 2002) in PROC GLIMMIX and considered models within 2.0 AICc units of the best approximating model competitive. We did not include a cova- riate in nest success models identifying habitat use at nest sites because this information did not exist for all monitored females. Therefore, we used G-tests to evaluate nest success with respect to habitat types in the immediate vicin- ity of the nest bowl (i.e., vegetative class at the Table 1. Description of nesting habitats classified at the Prairie Plan site of the Metropolitan Water Reclama- tion District of Greater Chicago (MWRD) in west-central Illinois, 2001–2003. Habitat type Description Cropland Row crop and small grain agriculture and stubble of previously cropped fields used for disposal of biosolids. Idle grassland Grasslands or planted cover not mowed during the growing season. Hay/idle mowed Vegetation cut for hay or mowed periodically during summer and typically included roadsides and odd areas. Forested Woody vegetation ≥ 6 m tall. Scrub Woody vegetation < 6 m tall. Pond Basins classified as palustrine habitats (≤ 2 m deep) by the National Wetlands Inventory (NWI) (Cowardin et al. 1979). Pasture Nonwoody vegetation used for livestock grazing. nest bowl) for nests located at MWRD during 1998–2003 (Table 1). We presented renesting effort and egg hatchability as simple propor- tions and compared these among years and be- tween age classes using G-tests; 2 x 2 compari- sons employed a Yates correction for continuity (Zar 1996). We used t-tests to compare first nest initiation dates between renesting females and unsuccessful females with only 1 nest at- tempt. We considered differences significant at P ≤ 0.05, and report means ± 1 SE. Hen, Brood, and Duckling Survival We calculated female survival encompassing the prenesting, nesting, and brooding periods using the Kaplan-Meier product-limit estima- tor modified for staggered entry (Kaplan and Meier 1958, Pollock et al. 1989, White and Garrott 1990). For determining survival, we censored females either the day following last radio contact, the day following transmitter loss, the day of brood loss, or the 20th day posthatch (Paquette et al. 1997). We used the Cox proportional hazards model (Proc PHREG, SAS Institute, Inc., Cary, NC; Kleinbaum 1996) to test for differences in survival in relation to year and female age. We estimated brood and duckling survival rates using the Kaplan-Meier product-limit estimator (Proc LIFETEST, SAS Nesting Biology of Mallards in West-central IllinoisSeptember 2009 7 Institute, Inc., Cary, NC), and used log-rank tests to compare brood survival between female age and among year classes (White and Gar- rott 1990:241). We censored 5 broods from brood survival estimates and 52 ducklings (6 broods) from duckling survival the second day posthatch due to transmitter and tracking failures. We pooled duckling survival across years 1998–2003 due to limited observations of ducklings. RESUlTS We captured 148 resident female Mallards and 61 males paired with radiomarked females during 1998–2003 (Table 2). The median age ratio of females was 0.66 yearling:adult, though values varied considerably. Breeding incidence was high with only 6 of 143 females (4.2%) not nesting. Five non-nesting females (83.3%) were yearlings, and the resulting age distribution for nesting females was 0.61 yearling:adult. Morphological Measurements and Body Condition Indices Breeding season body mass of male Mallards averaged 1,193 g (range: 980–1,370 g; Table 3). Mean body condition indices for males dif- fered among years (F5,60 = 3.14; P = 0.015) and was 8% greater in 2000 than 1999 (P ≤ 0.05). Table 2. Status, breeding incidence, capture rates, and age ratios of resident Mallards (Anas platyrhynchos) monitored in west-central Illinois, 1998–2003. Year Status 1998 1999 2000 2001 2002 2003 Resident females 28 37 32 12 19 20 Nested and tracked successfully 27 33 24 11 16 18 Did not nest 0 1 1 1 2 1 Died before nesting 0 2 1 0 0 1 Radio failure 1 1 4 0 0 0 Nested but unsuccessfully tracked 0 0 2 0 1 0 Breeding incidence (%)a 100.0 97.1 96.7 91.7 89.5 94.7 Capture rate (females/trap-day) 0.14 0.19 0.16 0.04 0.05 0.06 Age ratios (yearling:adult) 0.47 1.18 0.33 0.50 1.38 0.82 Resident malesb 10 16 9 4 11 11 a When determining breeding incidence, females that died (n = 4) or experienced transmitter failure (n = 1) prior to nesting were excluded (e.g., only 1 of 4 females in 2000 with a faulty radio transmitter was excluded because failure occurred prior to nesting). b Paired and captured with resident females. Female body mass differed among age classes (F1, 147 = 19.47; P < 0.001), but not years (F5,147 = 2.04; P = 0.077), and mean body mass of adults exceeded yearlings by 6% (Table 4). However, female body condition differed among years (F5,147 = 3.25; P = 0.008) and age classes (F1,147 = 8.70; P = 0.004). Post-hoc comparisons indicated that females were in better condition in 1998 (4.2 ± 0.1 g/mm) than 1999 (3.9 ± 0.0 g/mm), 2000 (4.0 ± 0.1 g/mm), 2001 (3.9 ± 0.1 g/mm), and 2002 (3.9 ± 0.1 g/ mm). Mean adult body condition (4.1 ± 0.0 g/ mm) was 4% greater than yearling body condi- tion (3.9 ± 0.0 g/mm) during 1998–2003. Nesting Parameters On average, the first Mallard nest of the season was initiated on 12 April, and the nesting season lasted 88 days. Typically, nests were terminated (i.e., hatched or destroyed) by 9 July (Table 5). One female initiated 4 nests in 1998, and all of these were unsuccessful. Mean num- ber of nests/nesting female within year and age classes was variable (Table 6), but a significant year/age interaction (F5, 126 = 2.92; P = 0.016) prevented interpretation of main effects. How- ever, adults (n = 79) generally initiated more nests (1.65 ± 0.08 nests/female) than yearlings (n = 48; 1.31 ± 0.08 nests/female; F1, 126 = 4.16; P = 0.044). Vol. 39 Art. 18 Illinois Natural History Survey Bulletin Ta bl e 3. M ea n ± SE m or ph ol og ic al m ea su re m en ts a a nd b od y co nd iti on in di ce s o f r es id en tb m al e M al la rd s ( An as p la ty rh yn ch os ) i n w es t-c en tra l I lli no is , 1 99 8– 20 03 . Ye ar B ill C ul m en 1 C ul m en 2 Ta rs us T ar su s To ta l W in g B od y co nd iti on d, e w id th c ( m m ) (m m ) ( m m ) w id th (m m ) le ng th (m m ) t ar su s ( m m ) M as s ( g) c ho rd (m m ) ( g/ m m ) 19 98 (n = 1 0) 24 .2 ± 0 .2 55 .1 ± 0 .8 6 3. 9 ± 0. 9 5 .3 ± 0 .1 4 7. 6 ± 1. 0 5 5. 3 ± 0. 8 1 ,2 23 .0 ± 2 6. 6 2 89 .0 ± 2 .9 4 .2 ± 0 .1 A B 19 99 (n = 1 6) 23 .9 ± 0 .2 56 .3 ± 0 .8 6 4. 0 ± 0. 8 5 .2 ± 0 .1 5 2. 0 ± 0. 5 5 6. 4 ± 0. 4 1 ,1 55 .6 ± 1 8. 5 2 90 .2 ± 2 .1 4 .0 ± 0 .1 B 20 00 (n = 9 ) 24 .0 ± 0 .2 54 .7 ± 1 .0 6 3. 6 ± 1. 2 5 .4 ± 0 .2 5 1. 7 ± 1. 0 5 7. 1 ± 0. 7 1 ,2 42 .2 ± 1 7. 7 2 89 .3 ± 1 .9 4 .3 ± 0 .1 A 20 01 (n = 4 ) 24 .3 ± 0 .5 56 .8 ± 1 .4 6 6. 8 ± 1. 5 5 .3 ± 0 .1 5 2. 7 ± 1. 0 5 7. 3 ± 0. 7 1 ,2 05 .0 ± 5 3. 2 2 88 .0 ± 2 .4 4 .2 ± 0 .2 A B 20 02 (n = 1 1) 24 .4 ± 0 .1 55 .5 ± 0 .7 6 4. 6 ± 0. 6 5 .2 ± 0 .1 5 2. 8 ± 0. 5 5 7. 0 ± 0. 4 1 ,2 01 .8 ± 1 9. 0 2 94 .5 ± 2 .0 4 .1 ± 0 .1 A B 20 03 (n = 1 1) 24 .2 ± 0 .3 55 .8 ± 0 .6 6 4. 0 ± 0. 7 5 .2 ± 0 .1 5 1. 4 ± 0. 6 5 7. 4 ± 0. 7 1 ,1 65 .5 ± 2 6. 4 2 92 .9 ± 1 .8 4 .0 ± 0 .1 A B a B ill a nd le g m ea su re m en ts d es cr ib ed b y B ye rs a nd C ar y (1 99 1) . b Pa ire d an d ca pt ur ed w ith re si de nt ra di o- m ar ke d fe m al es . c Sa m pl e si ze fo r b ill w id th in 2 00 0 w as re du ce d (n = 8 ) d ue to d ef or m iti es . d M as s ( g) /w in g ch or d (m m ). e M ea ns n ot sh ar in g a le tte r d iff er ed st at is tic al ly . Tu ke y/ K ra m er p os t h oc m ul tip le c om pa ris on s P < 0 .0 5. Mean initiation date for first nests varied during 1998–2003 (Table 7); for example, nest initiation was 2 weeks earlier in the spring of 1998 than during 1999 and 2002 (F5, 127 = 4.74; P < 0.001). However, nest initiation date did not differ by female age (F1,127 = 2.24; P = 0.137). The majority (75%) of all nests (n = 195) were initiated by 20 May during 1998– 2003 (Fig. 2); therefore, the majority of nests were predicted to hatch by 24 June. Incubated clutch size of 66 first nest attempts ranged from 4–12 eggs ( x = 9.4 ± 0.2 eggs) and did not differ by age (F1, 65 = 2.04; P = 0.158) or year (F5, 65 = 0.50; P = 0.777). Clutch size of 19 second nests averaged 8.8 ± 0.4 eggs, and 3 third nest attempts contained 10 eggs each. Mean clutch size for all nests was 9.3 ± 0.2 eggs (n = 88). We did not detect a relation- ship between incubated clutch size and nest ini- tiation date (F1, 87 = 3.15; P = 0.080), although the trend was generally declining (Fig. 3). Egg hatchability was 92.1% (n = 329 eggs; n = 37 hatched nests), ranging from 77.8% in 2001 to 97.6% in 1998, and was fairly con- sistent in other years (93.6% in 1999, 90.5% in 2000, 90.2% in 2002, and 95.5% in 2003). Yearlings hatched a greater proportion of eggs (97.3%; n = 109 eggs) than adults (89.6%; n = 220 eggs) (G1 = 4.93; P = 0.026). Overall, < 1 egg failed to hatch per successful nest (Photo 5). We evaluated renesting effort of 77 females that survived an unsuccessful first nesting at- tempt. The proportion of females each year that renested ranged from 50.0–85.7%, and adults were more likely to renest (75.0%; n = 52) than yearlings (48.0%; n = 25) (G1 = 4.36; P = 0.037). Additionally, renesting females ini- tiated first nests (n = 51; April 27; SE 1.4 days) earlier than those not renesting (n = 26; May 4; SE = 2.0 days) (t75 = 3.03; P = 0.003). We considered 3 of 4 models formulated to explain variation in nest survival to be com- petitive (∆AICc ≤ 2.0; Table 8). The best approximating model was the intercept-only model, which indicated a constant nest-survival rate of 19.6% during our study (Table 9). The second-best model was 0.5 AICc units from the best model and included NESTINIT, which suggested nest survival declined slightly over Nesting Biology of Mallards in West-central IllinoisSeptember 2009 9 Table 4. M ean ± SE m orphological m easurem ents a and the body condition indices of resident fem ale M allards (Anas platyrhynchos) in w est-central Illinois, 1998–2003. Year-age B ill C ulm en 1 C ulm en 2 Tarsus Tarsus Total W ing B ody class w idth (m m ) (m m ) (m m ) w idth (m m ) length (m m ) tarsus (m m ) M ass (g) chord (m m ) condition b ( g/m m ) 1998 A dult (n = 19) 22.6 ± 0.2 51.5 ± 0.6 59.3 ± 0.5 5.2 ± 0.1 47.2 ± 0.5 53.5 ± 0.4 1,141.1 ± 17.2 267.6 ± 1.6 4.3 ± 0.1 Yearling (n = 9) 23.2 ± 0.4 52.7 ± 0.7 60.0 ± 0.9 5.2 ± 0.1 47.9 ± 0.8 53.7 ± 0.7 1,078.9 ± 30.2 267.6 ± 2.7 4.0 ± 0.1 1999 A dult (n = 17) 23.0 ± 0.2 51.6 ± 0.5 58.2 ± 0.5 5.0 ± 0.1 48.7 ± 0.3 53.5 ± 0.3 1,087.7 ± 18.5 273.4 ± 1.7 4.0 ± 0.1 Yearling (n = 20) 23.2 ± 0.2 53.0 ± 0.4 59.7 ± 0.5 4.9 ± 0.1 49.1 ± 0.5 53.7 ± 0.5 1,041.5 ± 17.9 267.6 ± 1.5 3.9 ± 0.1 2000 A dult (n = 24) c 23.1 ± 0.2 51.3 ± 0.4 58.7 ± 0.5 5.1 ± 0.1 48.6 ± 0.5 54.0 ± 0.4 1,080.0 ± 16.0 274.2 ± 1.2 3.9 ± 0.1 Yearling (n = 8) 23.0 ± 0.1 51.4 ± 0.6 58.5 ± 0.7 5.0 ± 0.1 48.9 ± 0.9 54.4 ± 0.7 1,060.0 ± 25.6 267.4 ± 2.1 4.0 ± 0.1 2001 A dult (n = 8) 23.3 ± 0.2 51.1 ± 0.8 58.7 ± 1.0 4.9 ± 0.1 47.8 ± 0.9 53.2 ± 0.7 1,075.0 ± 33.9 274.1 ± 3.7 3.9 ± 0.1 Yearling (n = 4) 23.4 ± 0.5 51.2 ± 1.4 59.3 ± 1.8 5.3 ± 0.1 48.5 ± 1.3 53.6 ± 0.6 1,000.0 ± 56.0 260.8 ± 3.1 3.8 ± 0.2 2002 A dult (n = 8) 22.7 ± 0.2 52.6 ± 0.9 60.1 ± 0.6 5.1 ± 0.1 47.4 ± 0.6 52.9 ± 0.4 1,137.5 ± 28.6 276.4 ± 3.7 4.1 ± 0.1 Yearling (n = 11) 22.7 ± 0.2 51.2 ± 0.3 58.8 ± 0.4 5.0 ± 0.1 48.9 ± 0.4 53.9 ± 0.5 1,025.5 ± 28.9 269.5 ± 1.1 3.8 ± 0.1 2003 A dult (n = 11) 23.1 ± 0.2 53.3 ± 0.6 61.1 ± 0.6 5.2 ± 0.1 49.7 ± 0.6 54.2 ± 0.4 1,146.4 ± 29.2 277.7 ± 2.2 4.1 ± 0.1 Yearling (n = 9) 23.3 ± 0.2 52.7 ± 0.6 60.0 ± 0.7 4.9 ± 0.1 49.7 ± 0.6 54.6 ± 0.9 1,046.7 ± 29.1 270.0 ± 1.1 3.9 ± 0.1 a B ill and leg m easurem ents described by B yers and C ary (1991). b M ass (g)/w ing chord (m m ). c Sam ple size for bill w idth w as n = 23 due to a deform ity. Vol. 39 Art. 110 Illinois Natural History Survey Bulletin Table 5. Mallard (Anas platyrhynchos) nesting season dates and lengths in west-central Illinois, 1998–2003. Year First nest initiation Last nest hatched or destroyed Nesting season length (days) 1998 4 Apr 1 Jul 89 1999 6 Apr 17 Jul 103 2000 12 Apr 20 Jul 100 2001 14 Apr 30 Jun 78 2002 22 Apr 7 Jul 77 2003 17 Apr 6 Jul 81 Table 6. Number of nest attempts by resident Mallards (Anas platyrhynchos) in west-central Illinois, 1998–2003. Nest attempts Year Age Females Mean SE 1998 Adult 18 1.56 0.22 Yearling 8 2.13 0.23 1999 Adult 15 1.67 0.19 Yearling 17 1.12 0.08 2000 Adult 19 1.74 0.15 Yearling 5 1.40 0.24 2001 Adult 8 1.50 0.27 Yearling 3 1.33 0.33 2002 Adult 8 1.38 0.18 Yearling 8 1.13 0.13 2003 Adult 11 1.91 0.25 Yearling 7 1.00 0.00 Table 7. Julian day and date of nest initiation for first nest attempts by resident Mallards (Anas platyrhyn- chos) in west-central Illinois, 1998–2003. Julian daya Year n Date Mean SE 1998 25 22 Apr 112 A 2.5 1999 33 6 May 126 B 2.2 2000 25 30 Apr 120 AB 2.2 2001 11 29 Apr 119 AB 3.7 2002 16 6 May 126 B 2.2 2003 18 29 Apr 119 AB 1.4 a Column means not sharing the same letter differed significantly, Tukey/Kramer post hoc tests. Nesting Biology of Mallards in West-central IllinoisSeptember 2009 11 0 0.25 0.5 0.75 1 90 100 110 120 130 140 150 160 170 180 C um ul at iv e pe rc en t Julian day 1998 1999 2000 2001 2002 2003 Figure 2. Percentage of Mallard (Anas platyrhynchos) nests initiated by Julian day in west-central Illinois. April May June 3 4 5 6 7 8 9 10 11 12 13 90 100 110 120 130 140 150 160 170 C lu tc h si ze Julian Day y = 11.6 – 0.019x P = 0.080, n = 88 April May June Figure 3. Regression of clutch size on nest initiation date for Mallards (Anas platyrhynchos) in west-central Illinois, 1998–2003. Figure 2. Percentage of Mallard (Anas platyrhynchos) nests initiated by Julian day in west-central Illinois, 1998–2003. Figure 3. Regression of clutch size on nest initiation date for Mallards (Anas platy- rhynchos) in west-central Illinois, 1998–2003. Vol. 39 Art. 112 Illinois Natural History Survey Bulletin Table 8. Candidate models to explain variation in Mallard (Anas platyrhynchos) nest success in west-central Illinois, 1998–2003, ranked by second-order Akaike’s information criterion (AICc). Also included are the number of estimable parameters (K), -2 log likelihood score (–2 Log), and model weight (wi). Model K –2 Log AICc ∆AICc wi S(.) 2 186.8 190.9 0.0 0.462 S(NESTINIT) 3 185.3 191.4 0.5 0.356 S(AGE) 3 186.6 192.8 1.9 0.182 S(YEAR) 7 179.9 194.5 3.7 0.074 Table 9. Nest and hen success of Mallards (Anas platyrhynchos) in west-central Illinois, 1998–2003. Values are back-transformed logit estimates from generalized linear mixed models. Nest success Hen success Year n % LCL UCL n % LCL UCL 1998 38 26.3 14.7 42.5 26 38.5 22.0 58.1 1999 45 15.6 7.6 29.3 33 21.2 10.4 38.5 2000 41 9.8 3.7 23.4 26 15.4 5.8 34.8 2001 16 25.0 9.6 51.0 11 36.4 14.2 66.4 2002 21 33.3 16.7 55.5 17 41.2 20.9 65.0 2003 28 17.9 7.6 36.5 18 27.8 11.9 52.2 Yearlings 60 21.6 12.6 34.3 81 26.0 15.5 40.3 Adults 129 18.7 12.7 27.0 50 29.7 20.4 41.1 Overall 189 19.6 14.1 26.7 131 28.3 20.9 37.1 time; however, the confidence interval about the parameter estimate overlapped zero, indi- cating the relationship was weakly supported. The third-best model (∆AICc = 1.9; Table 8) included AGE, and indicated that yearling nest survival was slightly greater (21.6%) than that of adults (18.7%), but the difference was not supported due to overlapping 95% confidence intervals. The final model included only YEAR and captured only 7.4% of the model weight (wi; Table 8), suggesting the model was not supported. Coyotes (Canis latrans) and rac- coons (Procyon lotor) were the most commonly identified nest predators (Table 10). Nine of 200 nests (4.5%) failed as a result of nonre- searcher human activities (e.g., abandoned, mowed, hayed, trampled, and 1 nest failed after the hen was killed by an automobile); 4 of those were specifically lost to agricultural practices. Similar to models of nest success, the best approximating model of hen success was Photo 5. Hatched Mallard (Anas platyrhynchos) clutch at the Metropolitan Water Rec- lamation District of Greater Chicago (MWRD) near Cuba, Illinois. Photo by Aaron P. Yetter. Nesting Biology of Mallards in West-central IllinoisSeptember 2009 13 Table 10. Fate of Mallard (Anas platyrhynchos) nests in west-central Illinois, 1998–2003. Number of nests by year Nest fate 1998 1999 2000 2001 2002 2003 Total Hatched 10 7 4 4 7 5 37 Coyote (Canis latrans) 15 10 7 0 3 2 37 Raccoon (Procyon lotor) 8 3 5 2 4 0 22 Mink (Mustela vison) 0 0 1 1 0 0 2 Snake 1 3 1 1 1 0 7 Striped skunk (Mephitis mephitis) 0 0 1 0 0 0 1 Opossum (Didelphis virginiana) 0 0 1 1 0 0 2 Turtle 0 1 0 0 0 0 1 Unknown predator 7 19 25 6 4 20 81 Abandoneda 6 1 0 0 0 1 8 Mowed/hayed 1 3 0 0 1 0 5 Agricultural equipment 0 0 0 1 0 0 1 Railroad maintenance 0 0 0 0 1 0 1 Auto collisionb 0 0 0 0 1 0 1 Total 48 47 45 16 22 28 206 a Five nests were abandoned due to researcher disturbance in 1998 and one in 1999. These nests were used in analyses where appropriate. b One nest failed because the female was found dead on a roadway; a presumed roadkill. Table 11. Candidate models to explain variation in Mallard (Anas platyrhynchos) hen success in west-central Illinois, 1998–2003, ranked by second-order Akaike’s information criterion (AICc). Also included are the number of estimable parameters (K), -2 log likelihood score (–2 Log), and model weight (wi). Model K –2 Log AICc ∆AICc wi S(.) 2 155.9 160.0 0.0 0.674 S(AGE) 3 155.7 161.9 1.9 0.262 S(YEAR ) 7 149.8 164.7 4.7 0.065 Table 12. Apparent nest success, habitat availability, and habitat use of nesting Mallards (Anas platyrhyn- chos, n = 167 nests) at the Prairie Plan area of the Metropolitan Water Reclamation District of Greater Chi- cago (MWRD) in west-central Illinois, 1998–2003. Habitat Percent Percent Habitat type availability (%) Nests of nests hatched Cropland 27.3 4 2.0 25.0 Forest 24.2 5 2.9 0.0 Idle grassland 14.5 93 55.7 25.8 Hay/idle mowed 14.5 44 26.4 11.4 Pasture 10.0 10 6.0 20.0 Scrub 4.9 10 6.0 20.0 Pond 4.7 1 0.6 0.0 Vol. 39 Art. 114 Illinois Natural History Survey Bulletin the intercept-only model (Table 11), which indicated a constant hen success rate of 28.3% (Table 9). The model including AGE was 1.9 AICc units from the best model, and param- eter estimates suggested adults were slightly more successful than yearlings (Tables 9 and 11). However, confidence intervals overlapped considerably, indicating no substantial differ- ence between age classes. The third-best model included YEAR but captured only 6.5% of model weight (Table 11). We classified habitats at 167 nest sites at MWRD into 7 broad classifications (Table 12). Nest success did not differ among these categories (G6 = 6.90; P = 0.330), even though habitat-specific nest success ranged from 0.0 to 25.8%. Nest success was low in hay/idle mowed habitats (11.4%); however, only 5 of 39 nests (12.8%) that failed succumbed to me- chanical destruction (Table 10). Idle grassland was the most-used nesting habitat (56% of nests) and had the highest apparent nest success rate (Table 12). Hay/idle mowed areas con- tained 26% of nests, and when combined with idle grassland, these 2 habitat classifications hosted 82% of all Mallard nests. Although the difference in nest success between grass- land and hay/idle mowed was not statistically significant, this difference may have biologi- cal implications. Together, scrub and pasture contained 12% of nests. Wetland, forest, and cropland were rarely used, and all 4 nests in cropland were in rye (Secale cereale). Brood Size Mean brood size at hatch was 8.2 ± 0.3 duck- lings (range: 4–12; n = 37) and did not differ among years (F5,36 = 0.62; P = 0.686); how- ever, annual sample sizes were small (range: 4–10 broods/year). Brood size on the 17th day after hatch averaged 3.0 ± 0.6 ducklings (n = 21) including 7 females that experienced total brood loss; this value was 36.6% of the brood size at hatch. Survival Survival rates (20 days) for 32 broods during 1998–2003 ranged from 0.643 ± 0.210 (2002) to 1.000 ± 0.000 (2001) and did not differ among years (χ2 5 = 0.96; P = 0.966). The over- all brood survival estimate (n = 32) was 0.759 ± 0.081 and included 7 females that lost their entire brood (Photo 6, Fig. 4). We included 251 ducklings from 31 broods in survival analyses. The 20-day survival estimate was similar across years (χ2 5 = 9.61; P = 0.087) and averaged 0.413 ± 0.035. Most duckling mortality (63.4%, n = 131) occurred within 5 days of hatch (Fig. 4), and 94.4% of 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1 3 5 7 9 11 13 15 17 19 Days posthatch Brood survival Brood CI 95 Duckling survival Duckling CI 95 Brood survival = 0.759 (SE = 0.081) Duckling survival = 0.413 (SE = 0.035) Figure 4. Kaplan-Meier survival estimates of Mallard (Anas platyrhynchos) broods (n = 32) and ducklings (n = 251) in west-central Illinois, 1998–2003. Figure 4. Kaplan-Meier survival estimates of Mallard (Anas platyrhynchos) broods (n= 32) and duck- lings (n= 251) in west-central Illinois, 1998–2003. Nesting Biology of Mallards in West-central IllinoisSeptember 2009 15 mortalities occurred by the 13th day. Female survival during the breeding season ranged from 0.546–1.00 (Table 13) and did not differ by year (χ2 1 = 0.93; P = 0.335) or age (χ2 1 = 1.33; P = 0.248). Thirty-two of 148 females (21.6%) died during the prenesting and nesting periods, and none were lost during brood rear- ing. Female survival averaged 0.710 ± 0.096 during 1998–2003. Twenty-five females were killed during 160 unsuccessful nest attempts; thus, the probability of mortality associated with a nest failure was 15.6%. Recruitment We estimated that 125 of 303 ducklings sur- vived to 20 days posthatch. Assuming a 50:50 sex ratio and no difference in survival between sexes, 62 female ducklings survived the period. Because 32 nesting females died during 1998– 2003, we calculated that 1.9 female ducklings survived to 20 days for each female that died during the breeding season. Except for 1999, the number of female ducklings surviving to 20 days exceeded the number of nesting females that perished each year. However, 148 females were considered residents at the start of the breeding season, which resulted in the produc- tion of 0.4 female ducklings per female in the spring breeding population. Based on existing survival estimates for female Mallards banded in northern Illinois and Wisconsin and duckling survival estimates from this study, we deter- mined annual recruitment ranged from 0.302 to 0.672 female ducklings/hen (Table 14). As- suming constant female and duckling survival rates among years, we estimated a recruitment rate of 0.613 female ducklings/hen was neces- sary to maintain a stable breeding population in west-central Illinois. We acknowledge that if duckling mortality from 20 days to fledge was considerable our estimates of recruitment would be biased high. DISCUSSION Mass and Body Condition Body masses of prenesting Mallards in our study were comparable to those documented in New Jersey, Minnesota, and the Canadian Park- lands of Alberta, Saskatchewan, and Manitoba (Figley and Van Druff 1982, Zicus and Rave 1998, Arnold et al. 2002). Our findings were nearly identical to those of Bellrose (1980), who reported that adult females averaged 1,107 g and immatures 1,048 g, whereas adult and immature male Mallards averaged 1,247 g and 1,193 g, respectively. However, female body mass in our study was 8–9% less than assumed in the Mallard Productivity Model (1,200 g adults; 1,100 g yearlings) (Krapu and Doty 1979, Johnson et al. 1987). We suggest that the lack of high-quality emergent marshes and diverse wetland complexes in the strip-mined lands of west-central Illinois partially explains the lower prenesting body mass of Mallards in our study compared to prairie-nesting Mallards. The body condition of prenesting females during this study resembled the fall condition indices of hunter-harvested female Mallards in Illinois (Hine et al. 1996). However, body condition of hunter-harvested Mallards may be biased low (Greenwood et al. 1986, Reinecke and Shaiffer 1988, Dufour et al. 1993). Spring body condition may be of particular concern in west-central Illinois because condition of pren- esting females should have exceeded indices of fall-harvested Mallards. Nest Initiation Nest initiation dates for Mallards in our study were similar to other areas of North America, with variation between studies presumably due to latitude. Mallards in southeastern Il- Photo 6. Mallard (Anas platyrhynchos) brood in west-central Illinois. Photo by Aaron P. Yetter. Vol. 39 Art. 116 Illinois Natural History Survey Bulletin Table 13. Kaplan-Meier survival estimates and 95% confidence intervals for resident female Mallards (Anas platyrhynchos) by age class in west-central Illinois during March–August, 1998–2003. Female No. of females Female Year age at risk failed survival 95% CI 1998 Adult 19 4 0.624 0.249 – 0.999 Yearling 9 2 0.750 0.472 – 1.000 Combined 28 6 0.672 0.364 – 0.980 1999 Adult 17 3 0.716 0.411 – 1.000 Yearling 20 9 0.546 0.328 – 0.763 Combined 37 12 0.599 0.337 – 0.862 2000 Adult 24 4 0.793 0.589 – 0.997 Yearling 8 1 0.857 0.617 – 1.000 Combined 32 5 0.800 0.612 – 0.987 2001 Adult 8 3 0.612 0.307 – 0.917 Yearling 4 0 1.000 – Combined 12 3 0.736 0.502 – 0.971 2002 Adult 8 1 0.875 0.661 – 1.000 Yearling 11 2 0.796 0.546 – 1.000 Combined 19 3 0.817 0.620 – 1.000 2003 Adult 11 1 0.909 0.747 – 1.000 Yearling 9 2 0.735 0.454 – 1.000 Combined 20 3 0.807 0.634 – 0.981 1998–2003 Combined 148 32 0.710 0.522 – 0.897 linois initiated nests between the last week of March and the first week of April (Louis 1999), whereas those in central California nested earlier, beginning in late February (McLandress et al. 1996). Mallards in Wisconsin initiated nests during the first week of April (Wheeler and March 1979), and nest initiation peaked the second week of May (Evrard 2002). Likewise, Mallards in northern Iowa had mean nest initia- tion dates of 11–21 May, with a range of 10 April–4 July (Fleskes 1986), and the onset of the Mallard nesting season in North and South Dakota was 8 April (Krapu et al. 2004). The Mallard Productivity Model assumes a 120-day nesting season for determining recruit- ment in the Prairie Pothole Region (Johnson et al. 1986). This value exceeded the longest nesting season we observed by 17 days; how- ever, a few unmarked females were known to be incubating nests well into July during our study (e.g., based on incidental brood sightings in August). In central North Dakota, Cowardin et al. (1985) identified a median nest initia- tion date of 18 May for adult and 20 May for yearling Mallards, and a median initiation date of 16 May was identified in Prairie Canada (Greenwood et al. 1995). In contrast, we found 75% of nests were initiated by 20 May. Similar to our findings, ducks initiated nesting in North Dakota roadsides during the third week of April. Only 4 nests were initiated after the first week of July, and all waterfowl nests were ter- minated by the second week of August (Voor- hees and Cassel 1980). We suspect the shorter nesting season we observed, along with the previously discussed female body condition, may reflect the quality of strip-mined wetlands in west-central Illinois when compared with marshes of the Prairie Pothole Region. Nesting Biology of Mallards in West-central IllinoisSeptember 2009 17 Table 14. Estim ates of param eters (SE) used to calculate recruitm ent (R ) and change in population (C ) for breeding M allards (Anas platyrhynchos) in w est- central Illinois, 1998–2003. Year Param eter 1998 1999 2000 2001 2002 2003 H en success 0.385 0.212 0.154 0.364 0.412 0.278 D uckling survival a 0.413 (0.035) 0.413 (0.035) 0.413 (0.035) 0.413 (0.035) 0.413 (0.035) 0.413 (0.035) B rood size at hatch 8.2 (0.9) 8.3 (0.6) 9.5 (0.9) 7.0 (1.1) 7.9 (0.7) 8.4 (0.5) R ecruitm ent (R ) b 0.651 0.364 0.302 0.526 0.672 0.482 A dult fem ale survival c 0.520 (0.029) 0.520 (0.029) 0.520 (0.029) 0.520 (0.029) 0.520 (0.029) 0.520 (0.029) Juvenile fem ale survival c 0.556 (0.049) 0.556 (0.049) 0.556 (0.049) 0.556 (0.049) 0.556 (0.049) 0.556 (0.049) Fem ale sum m er survival d 0.710 (0.096) 0.710 (0.096) 0.710 (0.096) 0.710 (0.096) 0.710 (0.096) 0.710 (0.096) Population change (C ) 1.030 0.805 0.756 0.932 1.046 0.897 a D uckling survival w as estim ated for 251 ducklings to 20 days posthatch and pooled across year and age classes. b Fem ale ducklings surviving to 20 days posthatch per nesting fem ale in spring. c Sm ith and R eynolds (1992:312). d Fem ale sum m er survival w as estim ated from 148 fem ale M allards m onitored during 1998–2003. Nesting Attempts The number of nesting attempts (n = 1.52) in west-central Illinois was slightly lower than previously published findings. In the aspen parklands of Canada, female Mallards carry- ing radio transmitters similar to those used in our study, initiated 1.44 nests/female, whereas females with abdominally implanted transmit- ters averaged 2.01 nests/female (Paquette et al. 1997). Mallards carrying abdominally implant- ed transmitters initiated 2.07 nests/female in southern Ontario (Hoekman et al. 2006a), and McPherson et al. (2003) reported 1.41 nests/ female from Mallards fitted with abdominally implanted transmitters in Alberta, Canada. However, McPherson et al. (2003) estimated they failed to detect 26% of the initiated Mal- lard nests, resulting in a corrected estimate of 1.91 nests/female. Our estimates of nest attempts should be considered conservative because external radio transmitters may have reduced nesting effort (Paquette et al. 1997). Additionally, some nest attempts may have gone undetected if nests were destroyed during early laying (McPherson et al. 2003); however, we monitored females daily and believe the number of undetected nests was low. The Mallard Productivity Model predicted that 1.18 to 2.14 nests/female will be initi- ated in conditions ranging from dry to wet in a given year in the glaciated prairies of North America (Johnson et al. 1986). Our analysis of nesting attempts included a significant interac- tion between year and age class that prevented main-effects comparisons; however, our data did not indicate that a relationship existed between precipitation and nest attempts, despite considerable variation in rainfall at MWRD during January–May of the study period (range: 28 to 58 cm; Josh DeWees, Metropolitan Water Reclamation District of Greater Chicago, pers. comm.). Nesting effort by adult females in 1998 was less than yearlings because 8 of 10 successful nests were hatched by adults, and 7 of these females hatched their first nest attempt. Thus, more adults successfully nested on their first attempt in 1998, thereby reducing renest- ing effort. Vol. 39 Art. 118 Illinois Natural History Survey Bulletin Clutch Size Clutch size in Mallards has been extensively documented, and the average clutch size in our study (9.4 eggs) was within the documented range. In a concurrent Mallard investigation in southeastern Illinois, Louis (1999) recorded an average clutch size of 10.7 eggs. Mal- lards averaged 9.7 eggs/clutch in the suburban environments near Chicago, Illinois (R.A. Montgomery, Max McGraw Wildlife Foun- dation, pers. com.). Bellrose (1980) noted that clutch size in Mallards was variable and averaged 9.0 eggs/clutch. Other investigations from throughout North America reported aver- age clutch sizes ranging from 7.1 to 11.7 eggs (Figley and Van Druff 1982, Krapu et al. 1983, Cowardin et al. 1985, Fleskes 1986, Clark et al. 1988, Krementz et al. 1992, Dwyer and Baldas- sarre 1993, McLandress et al. 1996, Yerkes and Bluhm 1998, Zicus and Rave 1998, Artmann 1999, Riviere 1999, Petrie et al. 2000, Nelson and Wetzel 2001, Ball et al. 2002, Evrard 2002, Zicus et al. 2003a, Hoekman et al. 2006a, Co- luccy et al. 2008). Mallard clutch size is believed to be nega- tively associated with nest initiation date and successive nest attempts (Johnson et al. 1987, McLandress et al. 1996). Declines in Mallard clutch sizes of 0.02 to 0.07 egg/day during the nesting season were reported in North Dakota, Minnesota, and California (Krapu et al. 1983, Cowardin et al. 1985, McLandress et al. 1996, Ball et al. 2002, Zicus et al. 2003a). We did not detect a trend in the incubated clutch size with increasing nest initiation date, but the relation- ship approached significance (P = 0.080). Females generally laid 1 egg/day, and we documented 4 occasions when females skipped laying during inclement weather, which occurs commonly among North American dabbling ducks (tribe Anatini; Alisauskas and Ankney 1992). Interestingly, we observed 1 female that failed to lay an egg for 5 consecutive days be- fore returning to complete her clutch and hatch 10 of 11 eggs. Egg Hatchability The average egg-success rate (i.e., hatchability; 92.1%) in our study was comparable to rates previously reported. For example, Bellrose (1980) compiled data from various studies and reported an egg success rate of 93.8%. Mal- lards hatched 89.1% of eggs during the mid- 1980s in north-central Montana (Orthmeyer and Ball 1990), and hatching success was 93.8–97.7% in Minnesota (Zicus et al. 2003b). Mallards at Union Slough National Wildlife Refuge in northern Iowa had an unusually high egg success rate of 99.0% (Fleskes 1986). Because estimated egg hatchability during our study was similar to previously reported estimates, we believe egg success did not limit Mallard recruitment in west-central Illinois. Renesting Effort Mallards will renest when adequate forage is available (Bellrose 1980, Titman 1981, Swanson et al. 1985), and captive wild Mal- lards have been induced to lay up to 5 clutches following egg removal (Swanson et al. 1986). Renesting effort by Mallards (50.0–85.7%) in our study was similar to the renesting rate of females with destroyed nests in Vermont (57%; Coulter and Miller 1968) and New Brunswick (50%; Petrie et al. 2000). In contrast, Dzubin and Gollop (1972) estimated lower renesting rates (30–48%) by Mallards in Saskatchewan and Manitoba, and Bergmann et al. (1994) de- tected no renesting of females with failed nests in eastern South Dakota. However, backpack radio transmitters used in their study have been demonstrated to negatively influence breed- ing effort in dabbling ducks (Pietz et al. 1993, Rotella et al. 1993). Based upon results from these studies, we suggest that renesting rates of Mallards we observed were adequate to sustain Mallard populations in west-central Illinois. Double-brooding is commonly defined as successfully hatching 2 nests in a breeding season. This phenomenon is considered rare in wild Mallards, but may be more common in suburban areas (Errington 1934, Figley and Van Druff 1982). Indeed, Mallards nesting in urban New Jersey commonly renested after total brood loss (Figley and Van Druff 1982). Double brooding by wild Mallards has been reported by Doty (1975) in North Dakota, Stafford et al. (2001) in South Dakota, and Ol- Nesting Biology of Mallards in West-central IllinoisSeptember 2009 19 sen et al. (2003) in Ohio. No females who lost their broods renested during our study. Continuous laying by Mallards is also uncom- mon. However, Arnold et al. (2002) reported that 9.1% (n = 3,064) of radiomarked Mallards renested immediately after an unsuccessful nest attempt. We documented continuous laying by only 1 of 77 (1.3%) females surviving an unsuccessful first-nest attempt. Nest Success Annual estimates of nest success in west- central Illinois ranged from 9.8 to 33.3% and averaged 19.6%. Bellrose (1980) reported that apparent nest success of Mallards was 24.8% in the Great Lakes states, which was somewhat greater than our estimate. Hoekman et al. (2006a) estimated nest survival of 13.0% for Mallards in southern Ontario, and Greenwood et al. (1987) reported relatively low nest suc- cess (12%) in Prairie Canada, concluding that nest success was least during drought years. Conversely, Drever et al. (2004) modeled duck nest success in the Prairie Pothole Region over many years (1935–2000) and suggested nest success may have been greater during or short- ly after drought years. The authors implied that this may have been due to drought-related changes in predator dynamics or because water- fowl populations contained more experienced adult breeders in dry years. Clearly, the rela- tionship between precipitation and nest success is somewhat uncertain. Nonetheless, we note that nest success during our study was least (9.8%) during the driest year and with the low- est age ratios (0.33 yearlings:adult). However, many factors (i.e., wetland dynamics, predator communities, and breeding duck densities) may be contributing to these differences in nest suc- cess rates. Beauchamp et al. (1996) reported that Mayfield-corrected estimates of nest success of 5 species of ducks in the prairies had declined compared to rates (21–33%) observed during the 1930s and 1950s. This reduction was par- tially attributed to habitat loss and agriculture (Cowardin et al. 1985, Klett et al. 1988, Green- wood et al. 1995, Beauchamp et al. 1996). Al- though we estimated grasslands (idle grassland and hay/idle mowed areas) represented 29% of the landscape at MWRD, much of Illinois’ tallgrass prairie has been destroyed (Neely and Heister 1987, Illinois Department of Energy and Natural Resources 1994). We suggest that the low quality of grassland vegetation (i.e., smooth brome and meadow fescue), combined with extensive mowing and haying activities at MWRD, likely suppressed nest success rates in our study. Some authors have suggested that duck nest success is dynamic and may decrease with increasing nest density (Livezey 1981, Fleskes 1986, Evrard 2002). We observed a similar trend, although nest densities we observed were generally less than the aforementioned studies. Specifically, nest survival was lower (9.8 to 26.3%) during 1998–2000, when the density of breeding Mallards (indicated by the female cap- ture rate; Table 2) was greatest. Nest survival was greater during 2001–2003 (17.9–33.3%) when we perceived lower breeding densities. Nest success has been identified as the most critical component of duck production (Cow- ardin and Johnson 1979, Cowardin et al. 1985, Johnson et al. 1987, Klett et al. 1988, Hoekman et al. 2002). We reviewed published estimates of nest success from various regions, years, and methods (Table 15) and found that Mallard nest success was highly variable. In their landmark study conducted in North Dakota, Cowardin et al. (1985) estimated Mallard nest success (Mayfield-Johnson) at 8.5% in agricultural environments; they predicted that a nest suc- cess rate of 15% was needed to maintain stable Mallard populations in that state. Gatti (1987), however, suggested that Mallards in Wisconsin required a 20% Mayfield nest success rate to maintain stable populations. Similarly, Evrard (2002) described a stable Mallard breeding population in Wisconsin that had an estimated Mayfield nest success rate of 21.6% during 1982–1990. Nest survival in west-central Il- linois was similar to these levels (15.6– 33.3%) in most years, but fell well below these thresh- olds in 2000. Nesting Habitat Use Mallards will nest in a variety of standing, Vol. 39 Art. 120 Illinois Natural History Survey Bulletin Table 15 continued on next page Table 15. Comparison of Mallard (Anas platyrhynchos) nest success rates from various geographic locations, methods of calculation, and years, 1952–2003. Success Source Location Methoda Years rate (%) Lee et al. 1964 Minnesota Apparent 1957–1960 31–42 Duebbert 1969 South Dakota Apparent 1968 82.6 Smith 1971 Alberta Apparent 1952–1965 42 Stoudt 1971 Saskatchewan Apparent 1952–1965 30 Voorhees and Cassel 1980 North Dakota Apparent 1968–1973 47 Cowardin et al. 1985 North Dakota Mayfield-Johnson 1977–1980 8.5 Fleskes 1986 Iowa Mayfield 1984–1985 9 Greenwood et al. 1987 Alberta, Saskatchewan, Mayfield-Johnson 1982–1985 12 and Manitoba Klett et al. 1988 Western Minnesota Mayfield-Johnson 1980–1984 5 Eastern North Dakota Mayfield-Johnson 1966–1984 5 Central North Dakota Mayfield-Johnson 1966–1984 8–11 Eastern South Dakota Mayfield-Johnson 1966–1984 9–10 Central South Dakota Mayfield-Johnson 1966–1974 19 North Dakota Apparent 1966–1984 7 Clark et al. 1991 Saskatchewan Mayfield-Johnson 1980–1986 1–45 Lokemoen and Woodward North, and South Dakota, Apparent 1985–1986 58 1992 and Montana Arnold et al. 1993 Minnesota, Manitoba Mayfield-Johnson 1985–1991 12.2–43.9 Dwyer and Baldassarre 1993 Northern New York Mayfield-Johnson 1990–1991 51 Kantrud 1993 Minnesota and North Dakota Mayfield-Johnson 1989–1991 9.7–25.1 Mauser and Jarvis 1994 Northern California Mayfield-Johnson 1988–1990 25.4–68.8 Greenwood et al. 1995 Canadian Prairie Potholes Mayfield-Johnson 1982–1985 11 LaGrange et al. 1995 North-central Iowa Mayfield-Johnson 1978–1990 14–39 Shaffer and Newton 1995 North, and South Dakota, Mayfield-Johnson 1966–1989 6–20 and Minnesota Kruse and Bowen 1996 Northwestern North Dakota Mayfield-Johnson 1980–1988 34.5 Maxson and Riggs 1996 West-central Minnesota Mayfield 1985–1987 3.9 McLandress et al. 1996 California Mayfield-Johnson 1985–1989 6.3–75.4 Nesting Biology of Mallards in West-central IllinoisSeptember 2009 21 Table 15 continued from previous page Success Source Location Methoda Years rate (%) Louis 1999 Illinois Mayfield 1997–1998 65 Riviere 1999 California Mayfield-Johnson 1994–1995 35.0–45.4 Petrie et al. 2000 New Brunswick Apparent 1992–1994 31 Huseby et al. 2001 Northwest Minnesota Apparent 1993–1995 23 Mayfield-Johnson 1993–1995 9.8 Nelson and Wetzel 2001 Pool 8 Mississippi River, Apparent 1981–1999 35–87 Wisconsin Reynolds et al. 2001 North-central United States Mayfield-Johnson 1992–1995 12.1–13.6 Evrard 2002 Wisconsin Mayfield-Johnson 1982–1990 21.6 Hoekman et al. 2006a Southern Ontario Known Fate Models 1997–2000 13 Program MARK Zimmerling et al. 2006 Eastern Ontario Apparent 1999–2001 83–90 Davis 2008 Great Lakes states Program MARK 2001–2003 15.6 a Mayfield 1961, 1975; Johnson 1979; Klett et al. 1986 dense vegetation types (Bellrose 1980), and the Mallard Productivity Model predicted that 35.6% of nests were located in grassland habitats under average hydrologic conditions in the glaciated prairies (Johnson et al. 1986). In North and South Dakota and Minnesota, planted cover (i.e., vegetation established for wildlife or soil protection) was the preferred duck-nesting habitat (Klett et al. 1988). De- spite limited areas of dense nesting cover at MWRD, our results were consistent with this trend, in that idle grassland (predominantly smooth brome) was the most frequently used nesting habitat and comprised 14.5% of the available nesting cover (Table 12). Forage crops, such as alfalfa, provide suitable nesting cover if mowed later in spring (Lee et al. 1964); however, first hay cuttings in Illinois occur earlier now than in previous decades. Warner and Etter (1989) reported that the mean date of first hay cutting in east-central Illinois was 9 June in 1951, but preceded 1 June by 1986–1987. During our study, the first hay cut- ting occurred at the peak of the Mallard nesting season with over 63% of alfalfa hay in Illinois harvested by 10 June and more than 85% cut by 20 June (Illinois Agricultural Statistics Service 2004). We suspect the lower use of hay/idle mowed areas compared with grasslands in our study was due to the lack of residual nesting cover in early spring, likely a result of third hay cuttings that occurred in August and Septem- ber 1998–2003 (Illinois Agricultural Statistics Service 2004). Farming operations in North and South Da- kota and Minnesota resulted in 27% of the duck nest failures in hayfields (Klett et al. 1988). Further, failure of nests in haylands was linked primarily to destruction by machinery in North Dakota; excluding mechanical mortality, nest success in hayfields was 82.4% (Cowardin et al. 1985). Surprisingly, only 4 of 31 (12.9%) Mallard nests in hayfields during our study were destroyed by agricultural machinery, although many nests were depredated prior to haying operations. Vol. 39 Art. 122 Illinois Natural History Survey Bulletin Many ducks nest in roadside right-of-ways in North and South Dakota and Minnesota (Hig- gins 1977, Voorhees and Cassel 1980, Sargeant 1981, Cowardin et al. 1985, Zicus and Rave 1998). We classified most roadside habitat as idle mowed, and found only 10 of 167 (6.0%) nests along roadsides, although several nests were located in idle grasslands near (< 50 m) roads. A common practice in Illinois was to mow roadsides many times during the grow- ing season. Clearly, roadside grasslands would provide better nesting habitat if mowed only once each year, especially if mowing occurred after the nesting season (i.e., August; Herkert et al. 1993). We found few overwater Mallard nests during our study. However, marsh nesting by Mallards was relatively common in Minnesota and the Great Lakes Region (Maxon and Riggs 1996, Davis 2008), and Cowardin et al. (1985) found 16% of nests of telemetered hens in wet- lands in North Dakota. Mallard use of wetland vegetation for nesting was associated with dry years, when upland cover was limited (Cow- ardin et al. 1985). Conversely, Krapu et al. (1979b) reported that 66% of observed Mallard nests in North Dakota were located in wetlands, and indicated that wetland nesting was more common in wet years. Success of overwater nests can be high; Arnold et al. (1993) reported success of wetland nests in Manitoba was 3.6 times greater than upland nests. Prior coal mining activities at MWRD resulted in many wetlands with bottom contours that prohibited robust emergent vegetation, limiting opportuni- ties for wetland nesting. Hen Success Hen success may be the best predictor of recruitment in birds, and Cowardin et al. (1985) estimated that a hen success rate of 31%, similar to the 28.3% observed in our study, was required for stable Mallard populations in North Dakota. Similarly, the Mallard Produc- tivity Model predicted stable populations in the prairies with a hen success rate of 28% under various assumptions of wetland conditions, female homing, and duckling survival (John- son et al. 1986). Our estimates of hen success approached or exceeded this threshold in 4 of 6 years. As with nest success, literature estimates of hen success indicated substantial spatial vari- ability. Outstanding hen success rates were ob- served in northern California (44–76%; Mauser and Jarvis 1994), New York (67%; Dwyer and Baldassarre 1993), and New Brunswick (39%; Petrie et al. 2000), and recent estimates of hen success in Ontario ranged from 25.4–46.0% (Hoekman et al. 2006a, 2006b). In contrast, Mallard hen success was only 15.2% in North Dakota (Cowardin et al. 1985) and 18.4% in the parklands of Canada (Paquette et al. 1997). Thus, we suggest that hen success in west-cen- tral Illinois exceeded some previously reported estimates from the prairies and parklands, and was sufficient in some years to promote popula- tion stability and growth. Brood Size Initial brood size (8.2 ducklings) in west- central Illinois was similar to investigations in North Dakota (6.8 ducklings; Talent et al. 1983) and south-central Saskatchewan (7.2–8.5 ducklings; Gendron and Clark 2002). How- ever, urban Mallards in New Jersey had initial brood sizes of 7.8 to 10.0 ducklings (Figley and Van Druff 1982), and even greater initial brood sizes were observed in Iowa (9.6 ducklings; Fleskes 1986) and Wisconsin (9.0 ducklings; Evrard 2002). We believe initial brood size did not limit Mallard recruitment in west-central Illinois. Survival Our estimate of Mallard brood survival to 20 days was 0.76 and comparable to results from previous studies. For example, Yerkes and La- Farge (2002) reported that brood survival was 0.47 and 0.87 in Ohio and Michigan, respec- tively. Sixty-day brood survival was estimated at 0.72 for ducklings exiting nest structures in New York (Weik and Malecki 1999). Broods exiting overwater nesting structures had sur- vival rates (≤ 20 days) ranging from 0.71 to 1.00 in South Dakota (Stafford et al. 2002). Mallard brood survival in Manitoba was better in wet than dry years (range: 0.34 to 0.70, Rotella and Ratti 1992a). Supporting this notion, Mallard broods in the Canadian Prairie- Parklands selected permanent and semiperma- Nesting Biology of Mallards in West-central IllinoisSeptember 2009 23 nent wetlands on their ability to retain water throughout the brood-rearing season (Raven et al. 2007). However, females with nests near permanent wetlands in California were less successful at fledging young than females nesting near seasonal wetlands, which provided higher quality brood habitat (Mauser et al. 1994b, Krapu et al. 2000). Our study area had many semipermanent and permanent wetlands that were available during drought, and some appeared to provide high-quality brood habitat (i.e., adequate escape cover and abundant invertebrate forage). However, seasonal wet- lands were less common, and many lacked the vegetative structure of prime brood-rearing ar- eas. Consequently, Mallard broods at MWRD were likely drawn to vegetative structure that provided escape cover rather than water perma- nency. Nonetheless, we believe Mallard brood survival in west-central Illinois was sufficient for population growth when compared with previous research. Duckling survival (20 days) in the present study was 0.413 with most duckling mortality (94.4%) occurring within 13 days posthatch. Gendron and Clark (2002) reported an excep- tional 30-day duckling survival rate of 0.595 from south-central Saskatchewan, which they attributed to excellent habitat conditions. They documented that most duckling loss occurred during the first 14 days. In southern Ontario, 30-day survival was 0.40, with 77% of duck- ling mortalities occurring within 8 days of hatch (Hoekman et al. 2004). Similarly, 86% of duckling mortality occurred by 14 days posthatch in New York, even though ducklings hatched from overwater nesting structures (Weik and Malecki 1999). In contrast to Illinois, duckling survival to 30 days on the Chesapeake Bay was 14–28% (Krementz and Pendleton 1991), and 30-day duckling survival was only 0.22 for Mallards in southwestern Manitoba during the drought years of the late 1980s (Rotella and Ratti 1992a). Duckling survival in northern Califor- nia was 18.1% to 10 days posthatch when wet- lands were dewatered prior to peak hatch for moist-soil management practices (Fredrickson and Taylor 1982). However, survival (50 days) increased to 0.366 and 0.344 in 1989 and 1990, respectively, when wetlands remained flooded into June (Mauser et al. 1994a). Chouinard and Arnold (2007) estimated 30-day duckling sur- vival to be 24.8% during 1996–1997 in the San Joaquin Valley, California, and they found that broods preferred reverse-cycle wetlands that were flooded from March to August, a period when marshes are normally dry. The authors suggested reverse-cycle wetlands may have provided better food resources for ducklings in addition to escape cover when compared with more permanent wetland types. In poorer quality brood habitats, such as large reservoirs, Salyer and Willms (1997) reported duckling survival to fledging ranged from 0 to 35%, and concluded that high nest success was negated without quality brood habitat. Re- search has demonstrated that duckling survival varies with macroinvertebrate availability (Cox et al. 1998, Gunnarsson et al. 2004) and that macroinvertebrate availability increases as seasonally flooded ponds increase on the land- scape (Neckles et al. 1990). Therefore, Krapu et al. (2000, 2006) suggested Mallard brood and duckling survival is enhanced during wet years in part due to increased area of seasonal ponds offering abundant macroinvertebrates that ducklings rely on for food. Similar to Illinois, duckling survival to 56 days was 44% in New Brunswick (Petrie et al. 2000), and Huseby et al. (2001) reported that 42% of Mallard ducklings survived to fledge in a wild rice (Zizania aquatica) farming land- scape in northwestern Minnesota. In Saskatch- ewan, Pearse and Ratti (2004) estimated 30-day duckling survival at 57% in areas following predator removal, whereas their estimates were lower (36%) in areas without predator removal. Weik and Malecki (1999) observed a 60-day duckling survival rate of 36% in broods exiting overwater nesting structures. Similarly, Stafford and Pearse (2007) reported Mallard ducklings exiting overwater nesting structures in South Dakota experienced 30-day survival rates of 42–77%. They attributed higher survival at one study site to better quality emergent vegetation that likely served as better escape and thermal cover. Vol. 39 Art. 124 Illinois Natural History Survey Bulletin Duckling survival in our study was higher than reported estimates for some intensively farmed regions and areas experiencing drought; however, survival was considerably lower than reported for areas with high-quality, brood-rear- ing habitats. Hence, we speculate that duckling survival was limited by the lack of quality brood rearing wetlands at MWRD. Support- ing this notion, Krapu et al. (2006) determined that duckling survival was enhanced during wet years when the number of seasonal wetlands on the landscape increased. Further, Hoekman et al. (2004) recommended enhancement and restoration of seasonal wetlands to increase duckling survival in southern Ontario. Co- luccy et al. (2008) suggested management that improved duckling survival such as wetland rehabilitation and restoration was the most ef- ficient way to enhance Mallard populations in the Great Lakes Region. We believe duckling survival was sufficient for maintaining Mallard populations in west-central Illinois but survival could have been enhanced by managing for emergent vegetation on brood-rearing wetlands and restoring seasonal wetland habitats on the landscape. Female mortality, aside from hunting, is an important component of Mallard population dynamics (Sargeant et al. 1984). Recently, Hoekman et al. (2002) concluded that the popu- lation growth rate of mid-continent Mallards was most sensitive to nest success and female survival during the breeding season. Survival of females during nesting and brood rearing in west-central Illinois (0.71) was similar to estimates from other regions of North America. For example, Devries et al. (2003) found a 13-week female survival rate of 0.76 in the Canadian Prairie Pothole Region. Other studies have shown that female survival was 0.65 to 0.84 in eastern Canada (Hoekman et al. 2006a, 2006b), 0.70 to 0.77 in the aspen parklands of Canada (Paquette et al. 1997), 0.74 in the Great Lakes Region (Coluccy et al. 2008), 0.81 in North Dakota (Cowardin et al. 1985), and 0.75 in north-central Minnesota (Kirby and Cowar- din 1986). Some regions experienced exceptional breed- ing season survival. Most notably, 85.6% of females in New Brunswick survived the breed- ing season (Petrie et al. 2000), as did 88.0% of females in a forested environment of northern New York (Dwyer and Baldassarre 1993). These values contrasted the 50.9% summer sur- vival rate of females monitored in Minnesota (Zicus and Rave 1998). Regional differences in predator communities, the composition of upland nesting cover, and availability of forage in wetland habitats likely influenced female survival during the nesting season. We anticipated female survival might decrease during brood rearing, because there were few high-quality emergent wetlands that provided escape cover on our study site. However, we observed no mortality of females during the first 20 days of brood rearing, and consequently, our results contrast those of other studies. For instance, 2 of 22 females (9.1%) died during brood rearing in New York (Dwyer and Baldassarre 1993), and Weik and Malecki (1999) estimated female survival to be 0.798 while rearing broods. Bergmann et al. (1994) reported that 10 of 60 (16.7%) females died during brood rearing in eastern South Dakota. More similar to our findings, Mauser et al. (1994a) documented no mortalities of females during brood rearing in California, and survival of brooding females was high in Minnesota (94.3%) and New Brunswick (97%) (Kirby and Cowardin 1986, Petrie et al. 2000). Therefore, we believe Mallard recruitment in west-central Illinois was not limited by survival of brood- rearing females. Recruitment We did not conduct breeding pair counts during our study; nonetheless, we perceived a decline in the breeding Mallard population as evi- denced by lower capture rates of females dur- ing 2001–2003 compared to 1998–2000 (Table 2). Although speculative, the reduced number of breeding females on our study area may have resulted from poor recruitment in 1999 and 2000. Compared with the high capture rate achieved in 1999, apparent success in capturing resident females declined substantially dur- ing spring of 2001 through 2003. These lower capture rates reflected trends in our estimates Nesting Biology of Mallards in West-central IllinoisSeptember 2009 25 of recruitment and the proportional popula- tion change. Interestingly, a similar trend was identified by the North American BBS during 1998–2003 for Mallards in Illinois (Sauer et al. 2007). Alternatively, returning females in sub- sequent years may have been reluctant to enter decoy traps, thereby lowering capture rates. Fluctuations in resident Mallard populations in west-central Illinois during our study may have been indicative of Mallard population cycles in nontraditional breeding areas. Petrie (1999) and Simpson et al. (2005) suggested that wetlands of the Great Lakes Region were more stable than marshes of the Prairie Pothole Re- gion, allowing for more consistent population maintenance and growth. However, Simpson et al. (2005) cautioned that constant duckling survival should not imply constant rates of re- cruitment. The apparent decline in recruitment documented during the 1999 and 2000 breeding seasons suggested that the Mallard breeding population in west-central Illinois suffered a notable decrease. The breeding population partially recovered due to better hen success in 2001–2002, but the projected 2004 spring population remained well below the 1998 and 1999 population levels. Recruitment of female Mallards in west- central Illinois was highly variable. Likewise, Mauser and Jarvis (1994) found a highly vari- able recruitment rate (0.31–1.26) in northern California and suggested the Mallard popula- tion in their study was increasing based on an average recruitment rate of 0.83. Similarly, Mallard recruitment in Ontario (0.79–0.99) was considered sufficient for population main- tenance (Hoekman et al. 2006b). However, recruitment rates observed in North Dakota (0.27; Cowardin et al. 1985) and Iowa (0.49; Fleskes 1986) were not sufficient for popula- tion growth. Assuming the annual survival rates of female Mallards (adult 0.520, yearling 0.556) esti- mated by Smith and Reynolds (1992:312) for Wisconsin and Illinois were representative of Mallards in west-central Illinois, a recruitment rate of 0.613 was required to maintain a stable population on our study area. Consequently, a 36.4% hen success rate and a duckling survival rate of 0.413 would have achieved this level of recruitment. The Mallard population in west- central Illinois declined during our study when the 6-year pooled hen success rate of 28.3% was below the hypothesized level necessary for population maintenance. Several years of high nest success and recruitment may be needed for the Mallard population to recover following the years of poor recruitment we documented. CONClUSIONS AND MANAGEMENT IMPlICATIONS Most parameter estimates associated with Mallard reproduction and recruitment in west-central Illinois appeared to be within ranges observed in studies on nesting Mallards throughout North America. Based on estimated recruitment rates, hen success was adequate in 1998 and 2002 for population growth but was too low in the other years to maintain the population. In all but one year, female survival during the breeding season was comparable to other populations of Mallards in secondary production areas. Our data indicated that management prac- tices designed to increase nest success, hen success, and duckling survival would likely increase Mallard populations in west-central Illinois. These same parameters were identi- fied as driving the population growth rate in mid-continent Mallards (Hoekman et al. 2002), and duckling survival and nest success were important breeding season parameters for the Great Lakes Mallard population (Simpson et al. 2005, Coluccy et al. 2008, Davis 2008). Estab- lishing or protecting unfragmented grasslands (> 20 ha) in areas lacking forests should benefit Mallards in Illinois (Herkert et al. 1993); however, larger tracts (> 300 ha) were required to enhance duck nest success in the northern prairies (Clark and Nudds 1991, Clark et al. 1991, Phillips et al. 2003). Similarly, Reynolds et al. (2001) concluded that upland perennial cover in 40% of the landscape was needed to achieve Mallard nest success rates necessary for stable populations in North Dakota. Others have questioned the efficiency of management practices designed to increase nest success in Vol. 39 Art. 126 Illinois Natural History Survey Bulletin the Great Lakes states due to low breeding den- sities of Mallards and the fragmented nature of the landscape (Coluccy et al. 2008). Yet, Mal- lard populations in Illinois have increased in recent decades despite the lack of large contigu- ous areas of grasslands (> 300 ha); thus, larger tracts of grassland may not be as important to recruitment of Mallards in Illinois. Agricultural policies that convert farmland to grasslands and native habitats, such as the U.S. Department of Agriculture’s Conservation Reserve, Conser- vation Reserve Enhancement, and Wetland Reserve programs, should be instrumental in increasing populations of nesting waterfowl in Illinois. Grassland managers in Illinois should delay mowing until August to avoid destruction of Mallard nests. Upland nesting habitats should include a mixture of native warm and cool season grasses and forbs, and avoid monotypic stands of vegetation (Swanson and Duebbert 1989). In the absence of fire, prairie grasslands succeed rapidly to woody and undesirable nonindigenous vegetation (Voorhees and Cas- sel 1980, Johnson and Temple 1990, Kadlec and Smith 1992, Herkert et al. 1993, Schwartz and Hermann 1997, Askins 2000). Therefore, grassland vegetation in Illinois should be maintained, if possible, with prescribed burns conducted between mid-October to mid-March at least every 3 to 5 years. Grassland manipu- lations should be staggered so residual nesting cover ≥ 60 cm tall is available in all years, and burns should be rotated between fall and early spring. Although our estimates of brood and duckling survival in west-central Illinois were comparable to other Mallard production areas, the overall lack of emergent marshes with their associated escape cover and abundant aquatic invertebrates may have suppressed brood and duckling survival in west-central Illinois. In fact, Coluccy et al. (2008) identified duckling survival as one of the most important fac- tors influencing the population growth rate of the Great Lakes Mallard population. Ideally, wetlands of all types and of reasonable qual- ity, especially seasonal wetlands, should be restored or enhanced in close proximity to nesting areas (Swanson and Duebbert 1989, Afton and Paulus 1992, Rotella and Ratti 1992b, Simpson et al. 2005, Krapu et al. 2006, Raven et al. 2007, Coluccy et al. 2008, Davis 2008). A 50:50 interspersion of open water and emergent vegetation, such as broad-leaved cat- tail (Typha latifolia), American lotus (Nelumbo lutea), and softstem bulrush (Schoenoplectus tabernaemontani), is preferred in shallow basins to provide spacing for breeding pairs and courtship and high-quality brood habitat that offers escape cover and invertebrate for- age for ducklings (Weller and Spatcher 1965, Courcelles and Bedard 1979, Mack and Flake 1980, Talent et al. 1982, Kaminski and Prince 1984, Belanger and Couture 1988, Swanson and Duebbert 1989, Kadlec and Smith 1992, Sedinger 1992, Stafford and Pearse 2007). Wetlands and lakes at MWRD were typical of older strip-mined lands in that they were gener- ally stable, open-water bodies lacking emergent and submersed aquatic vegetation. Therefore, restoration and enhancement of emergent marshes and the aquatic invertebrates they sup- port would likely provide conditions to enhance Mallard recruitment in west-central Illinois. Further research is warranted to evaluate annual survival of females and ducklings in Illinois. Survival estimates of resident post- breeding females and post-fledging juveniles from banding and radiotelemetry investigations would provide better estimates of recruit- ment in Illinois. Indeed, nonbreeding survival was the most important parameter driving the population growth rate in other Great Lakes studies (Coluccy et al. 2008). Migratory pat- terns (including molt movements) of Illinois’ resident Mallards are largely unknown, and information on the relationship between cur- rent hunting practices (e.g., spinning-winged decoys) and harvest in Illinois and other states is needed to better understand Mallard popula- tion dynamics. West-central Illinois contains many man-made lakes and ponds that often lack shallow-water foraging sites and escape cover for ducklings; therefore, investigations of the energetics of breeding Mallards and broods in this region would provide information to aid future management, restoration, and rehabilita- Nesting Biology of Mallards in West-central IllinoisSeptember 2009 27 tion programs. Lastly, additional telemetry studies would provide insight into the effects of grassland establishment (filter strips and patch size), grassland management (burning, mowing, and haying), and current agricultural practices (conservation tillage and no-till) on nesting Mallards in Illinois. ACKNOWlEDGMENTS This study was supported through Federal Aid in Wildlife Restoration Project W-130-R with cooperation from the IDNR, INHS, and the U.S. Fish and Wildlife Service. The form, con- tent, and data interpretation are the responsibil- ity of the University of Illinois and the INHS. We thank J. Moore, T. Skuse, D. Prater, and staff at the Metropolitan Water Reclamation District of Greater Chicago and B. Douglass and J. Ball at the IDNR Banner Marsh State Fish and Wildlife Area for advice and assis- tance. The following INHS staff assisted with this project: P. White, B. Amdor, E. Whetsell, L. Anderson, R. Hillemeyer, J. Steckel, D. Strubing, B. O’Neal, A. Bartlett, and K. Roat. Veterinary consultation for radio-transmitter attachment was provided by the Institutional Animal Care and Use Committee (IACUC) at the University of Illinois at Urbana-Champaign (UIUC), and R. Yetter, D.V.M., Havana, IL. The Illinois Department of Transportation, Division of Aeronautics, Springfield, IL, and P. Mankin, UIUC, Department of Forestry, Urbana, IL, provided aerial support for the project. Game- farm Mallards used during decoy trapping were purchased from Whistling Wings, Inc., Ha- nover, IL. We thank L. Flake, L. Fredrickson, J. Levengood, and C. Warwick for their critical review of the manuscript. 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