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Why a Symposium About Timber Rattlesnakes?

Why the concern about a venomous species of snake that
shares home-space with humans in states along the

Upper Mississippi River? … [S]tudies reveal and confirm that
the species is losing its foothold along the Upper Mississippi and
its collateral river-bluffland corridors.

Timber Rattlesnakes once ranged from southern Maine to
Florida and westward to Minnesota and Oklahoma, down to
Texas.…

Timber Rattlesnakes were probably the first venomous
snake encountered by early settlers during their forays into the
forests and mountains of eastern North America. One of the ear-
liest explorers to our region, Father Louis Hennepin, noted rat-
tlesnakes as “serpens sonnettes” in his travel log during his Upper
Mississippi voyage in 1680. Shortly thereafter, in 1700, Leseur
mentioned the potential “danger” of rattlesnakes in the caves
around Lake Pepin. Two centuries later, the impact of increased
human settlement along the Mississippi on Timber Rattlesnakes
could be read about in local newspapers. One such article
reported the killing of hundreds of “rattlers” in a single day at
Minnesota’s Cedar Creek Bluffs (The Winona Daily Republican-
Herald; August 16, 1913). Similar events occurred at other sites

along the Upper Mississippi Valley, and human fear regarding
this abundance of dangerous rattlesnakes led to the implemen-
tation of a bounty system that served as an economic incentive
for the killing of Timber Rattlesnakes. The bounty system pro-
vided a viable source of income for some individuals during
years of hard economic times, and thousands of Timber
Rattlesnakes were killed. Their heads and rattles were turned in
for a fee. Bounty systems were eventually repealed in Wisconsin
and Minnesota, but not until 1975 and 1989, respectively.

Amazingly, for three centuries following the arrival of set-
tlers, the Timber Rattlesnake has managed to persevere despite
the continuous loss of its habitat to agriculture, the dissecting of
its habitat with roads, encroaching housing developments in
recent decades, and depredation by man. One cannot deny that

Timber Rattlesnake (Crotalus horridus) 
Biology and Conservation in the 
Upper Mississippi River Valley1

Saint Mary’s University of Minnesota

Winona, Minnesota
24 September 2005

Photographs by Barney Oldfield, www.lizardsandlandscapes.com

Excerpts from Abstracts.2

IGUANA  •  VOLUME 13, NUMBER 1  •  MARCH 2006 31TIMBER RATTLESNAKE SYMPOSIUM

�

An old adult male Timber Rattlesnake (Crotalus horridus) from Houston County, Minnesota.

1 Limited quantities of the complete program with extensive
“abstracts” and color photographs are available from Zoo Book Sales
(zoobooks@acegroup.cc) or visit their website: www.zoobook-
sales.com.

2 Daniel Keyler’s introduction is presented verbatim, with excluded
sections indicated by “…” Abstracts are summarized and occasion-
ally paraphrased for brevity.

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the Mississippi’s bluffs and valleys, which have been the Timber
Rattlesnake’s home for thousands of years, represent some of the
most beautiful landscapes in the country. However, the con-
stantly increasing interface between Timber Rattlesnake habitat
and humans has gradually taken its toll on the rattlesnakes over
time, and loss of Timber Rattlesnake habitat is accelerating.

Mutual coexistence between humans and rattlesnakes is
complex, but is essential if the Timber Rattlesnake is to retain its
place in the Upper Mississippi River Valley ecosystem…. If true
conservation of this species is not achieved in the near future,
the Timber Rattlesnake will fade from the Upper Mississippi
River Valley, becoming a legend of the past.

Daniel E. Keyler

Some Notes on Phenology, Reproduction, and 
Winter Biology of Timber Rattlesnakes in Wisconsin

Since 1999, Timber Rattlesnakes at several Wisconsin den sites
have been monitored with radio transmitters [see Iguana
12:90–97]. Three records of snakes emerging in early April may
have involved animals that were ill. The latest recorded den
ingress was 19 October.

Snakes moved within winter dens, reaching their deepest
penetrations during December and January. Lowest body tem-
peratures occurred from late March to early April. Movement
toward the den entrance began at about that same time.

Seven females monitored over five years produced 15
clutches. Mean interval between clutches was 3.14 years (range
2–5 years). The earliest recorded birth was 30 August, the latest
occurred in early October.

Craig Berg

Reproduction at a Northwestern Illinois 
Timber Rattlesnake Rookery

Since 1991, monitoring a Timber Rattlesnake rookery in north-
western Illinois has generated the following data: (1) Gravid

females arrived between 29 April and 21 July. (2) Postpartum
female departure ranged from 22 August to 30 September. (3)
Earliest neonate appearance ranged from 19 August to 15
September. (4) Latest dates for neonate emergence ranged from
28 August to 12 October. (5) Litter sizes ranged from 5–11 (total
of 106 births observed to date). (6) Of 18 reproductive cycles, 13
(72.2%) were 2 years and 5 (27.8%) were 3 years (mean = 2.28
years). Two females had both 2-year and 3-year cycles. (7) For 22
females, 10 (46%) gave single births during the monitoring
period, 8 (36%) gave birth twice, 2 (9%) gave birth 3 times, and
2 (9%) 4 times. (8) Many gravid females depart from the rookery
prior to parturition and give birth at undetermined locations. One
such location was about 30 m upslope from the rookery den.
Additional observations included: One mating event on 22
August 2001 in the vicinity of the rookery; interactions between
neonates and mothers, including cloacal posturing with scent ejec-
tion; interactions between gravid females, non-gravid females, and
males; rain-drinking by gravid females; and molting.

Habitat modification by burning and cutting around the
rookery resulted in the creation of an additional rookery that was
utilized by females from the original rookery. Such practices
might be used to restore historical basking/gestating/birthing
sites in blufflands that have become overgrown and shaded and
are no longer used.

Brian Bielema

Long-term Field Studies of the Timber Rattlesnake: 
What Has Been Learned?

A series of dens in the southeastern Adirondack Mountains of
New York have been under continuous study since 1978.
Resultant data and on-going conservation efforts allow this sys-
tem to serve as a microcosm of approaches taken to protect and
manage Timber Rattlesnakes anywhere in their range.

Den populations vary from 42–558 new individuals cap-
tured over a 25-year period. Although not population size esti-

32 IGUANA  •  VOLUME 13, NUMBER 1  •  MARCH 2006 TIMBER RATTLESNAKE SYMPOSIUM

An adult male Timber Rattlesnake (Crotalus horridus) from Houston County, Minnesota, showing classic sulphur coloring, black chevrons, velvet
black tail, and tan rattle.

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IGUANA  •  VOLUME 13, NUMBER 1  •  MARCH 2006 33TIMBER RATTLESNAKE SYMPOSIUM

mates, the data suggest a wide variation in numbers of snakes
using dens. Shifts between dens are rare. Estimated survival rate
in field-born snakes was about 65% in the first year, whereas
adults (5+ years old) survived at about 90% per year. Recapture
intervals of 22 and 23 years for snakes released initially as adults
(at least 10 years old when marked) suggest a natural lifespan
that approaches 35 years.

Five major range segments correspond to ecoregions. These
divisions may deserve targeted conservation attention based on
particular biological features associated with each region and its
subdivisions. Varying parameters of snake biology can guide
efforts within a management unit. For example, in the New
England Upland management unit (where the current study is
taking place), the snake is characterized by high adult survival
rates, low rates of reproductive performance brought on the
decadal span necessary for female maturity, and exceptional
longevity in some individuals. In contrast, snakes in the
Southeast Atlantic-Gulf Coastal Plains management unit would
require different strategies because adult survival rates may be
lower, reproductive performance higher or shifted to younger
age classes, and shorter longevity. Some management plans
should therefore stress steps to enhance survival, others to
enhance reproduction. Enhancing longevity might be achieved
by legal protection coupled with vigilance. To reflect such
regional variations, a national Timber Rattlesnake Conservation
Action Plan (TRCAP) was developed ten years ago. The chief
goal of the plan has been to produce a major synopsis of the his-
torical and current distribution, threats, and management
options authored at the state level by recognized authorities.
Those involved in TRCAP are hopeful that this plan will
become an exemplary model of a comprehensive conservation
strategy for the Timber Rattlesnake. Certainly, it is one of the
first for any reptile in North America.

William S. Brown

A History of Timber Rattlesnakes in 
Winona County, Minnesota

Detailed petroglyphs of rattlesnakes were traced by Theodore
Lewis in the 1880s from a cave in La Moille and artifacts from

a nearby rock shelter were attributed to the Woodland Tradition
(~2500–1000 years before present). Unfortunately, the petro-
glyphs are no longer extant. Tales from the 1800s tend to
emphasize the size of individual snakes and the sheer number of
snakes that were destroyed at certain localities. The most cele-
brated characters in the history of human interactions with rat-
tlesnakes were the bounty hunters of the 1900s. “Black Bill”
Venzol of Elba would bring rattlesnakes to the old schoolhouse
for the children to see, Raymond Carter of Pickwick caught 86
rattlesnakes from one spot in a single afternoon during the Great
Depression, and, across the border in Fillmore County, Arnold
Rank killed over 2000 rattlers during his long career.
Fortunately, times have changed. The bounty has been elimi-
nated, and bounty hunters have been replaced by rattlesnake
responders who remove nuisance snakes from yards and relocate
them to more natural habitats within their home ranges.

Philip A. Cochran

Timber Rattlesnake Work with 
Private Landowners in Minnesota

Triggered by increased frequencies of human-rattlesnake
encounters, the Minnesota Department of Natural Resources
(MN DNR) has been working with private landowners in
southeastern Minnesota on bluff prairie management and
Timber Rattlesnake management. The main reasons for
increased encounter rates are degrading habitat, habitat frag-
mentation, and encroaching land development.

The Timber Rattlesnake was listed as a threatened species
in Minnesota in 1996. Its range once covered all of the bluff
counties along the Mississippi River. Today, the active range is
reduced to remnant populations in Goodhue, Olmsted,
Wabasha, and Winona counties, with larger populations in
Fillmore and Houston counties — with most on private lands.
Many once active den sites are extirpated, and many currently
active dens are in jeopardy of extirpation.

Restoration of habitats involved clearing cedar-infested bluff
prairies in critical snake habitats. Initially, efforts were successful,
but slow, affecting only a few acres at a time. A new federal pro-
gram created by Congress in 2002, the Landowner Incentive

A Timber Rattlesnake raising its head in response to the approach of
the photographer (Winona County, Minnesota).

An adult female Timber Rattlesnake in a rock cranny with neonates,
which will stay with her up to two weeks. Note the opaque eyes of the
neonates prior to their first shed (Houston County, Minnesota).

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Program (LIP), administered by the U.S. Fish & Wildlife Service,
allocates funds to assist states in working with private landowners
on “at risk species.” LIP funds help landowners implement man-
agement practices that maintain, enhance, or restore habitats that
benefit bluff prairie “at risk” species. Practices include cedar
removal, invasive species control, and prescribed burning.

Jaime Edwards and Dave Spiering

Status of Timber Rattlesnakes in Wisconsin
Wisconsin Timber Rattlesnake populations appear to be signif-
icantly reduced from historic levels. Human persecution, includ-
ing a county-administered bounty system, has been a major con-
tributing factor. Records indicate that hunters targeted gravid
females, accelerating the population declines by restricting
recruitment. Other factors include den destruction and habitat
loss to agriculture. In recent years, natural succession has resulted
in overgrowth of prairies, specifically contributing to degrada-
tion or loss of overwintering or rookery sites.

The state has outlined a four-tiered approach to conserva-
tion that will be implemented as funding allows. One element is
an educational program for rural landowners called “Rare Snake
Workshops.” These help promote conservation of four prairie- or
bluffland-dwelling snakes, including the Timber Rattlesnake. As
of summer 2005, 58 workshops have been conducted. Each
addresses how to safely handle and move venomous snakes, why
habitat management is necessary, and the Department of Natural
Resource’s nuisance control program.

Additional conservation efforts include surveys to identify
and protect hibernation sites and support of research to better
understand this snake in Wisconsin.

Robert Hay

Timber Rattlesnake Bites in the 
Upper Mississippi River Valley

Two species of rattlesnakes, the Timber Rattlesnake (Crotalus
horridus) and Massassauga (Sistrurus catenatus) are native to the
Upper Mississippi Valley. Bites, albeit rare, do occur. Prior to
1880, 70 cases of venomous snakebite were reported in
Wisconsin. Twelve were fatal, five victims were men, four were
children, and three were women. Literature records indicate that
15 bites occurred in Wisconsin from 1958–59, but only four in
Minnesota.

More recent records show 36 cases of rattlesnake bite,
involving eight different species, in Minnesota, western
Wisconsin, and northeastern Iowa from 1982–2002 (1–2 bites
per year). Timber Rattlesnakes were responsible for 27 bites,
with 15 in Minnesota, seven in Wisconsin, and five in Iowa. All
bites occurred between April and October. Fewer than half
(44%) were naturally occurring bites; the rest resulted from
deliberate human manipulation of snakes. Most victims were
males (81%) and the average age was 33 ± 12 years. All victims
were evaluated in a medical facility, only 12 were hospitalized.
Fang punctures were evident in all patients, but symptoms of
envenomation were absent or minimal in 52% of victims. One
instance of intravenous envenomation was fatal. Venom-induced
effects were profound and occurred rapidly. Antivenin was
administered to 11 patients, two had surgery, and average hos-
pital stay was 3.5 days.

Daniel E. Keyler

Timber Rattlesnakes in Northeastern Iowa
Timber Rattlesnakes occur in northeastern, southeastern, and
small areas of central Iowa. Little information exists in the liter-

34 IGUANA  •  VOLUME 13, NUMBER 1  •  MARCH 2006 TIMBER RATTLESNAKE SYMPOSIUM

A very large adult male Timber Rattlesnake with a complete (tan) rattle and a black basal segment (Fillmore County, Minnesota).

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IGUANA  •  VOLUME 13, NUMBER 1  •  MARCH 2006 35TIMBER RATTLESNAKE SYMPOSIUM

ature regarding the species in the state and unpublished surveys
provide insubstantial baseline data. Consequently, trends are dif-
ficult to quantify.

Variations in morphology encompass the full range of what
is expected in the Upper Mississippi Valley. Ground color ranges
from golden yellow to tan or brown. A rust-red middorsal stripe
is almost always present, but may vary in intensity, especially
posteriorly. “Bow-tie” markings are common and often become
full bands toward the tail. Entirely gray specimens are known,
but are uncommon.

Emergence begins in late April to early May. Autumn stag-
ing is initiated in late September; ingress occurs by mid-October.
Individuals have been observed basking in mid-April, but those
animals usually show signs of dermatitis. Most adult males and
non-gravid females appear to migrate to summer feeding sites
7–15 days after first emergence. Gravid females select den sites,
rock crevices with significant depth or large loose rocks, as rook-
eries. Neonates to two-year olds seem to prefer loose rock in
small forest patches in or at the edge of prairies.

Reproductive data are scant. Nothing is known of courtship
or mating. Females produce litters at least biennially or trienni-
ally. Parturition usually occurs in late August or early September,
peaking during the first week in September. Litter sizes range
from 5–12, average of 8. Neonates range from 257–348 mm in
total length; average is 344 mm.

Bounty records from 1925–1952 show an obvious decline
in numbers, and conversations with bounty hunters indicate a
decline in snakes rather than a reduction in efforts to catch
them. Timber Rattlesnakes were unprotected in Iowa until
2001 (the only other reptile unprotected in the state was the

Garter Snake. Recent revisions of rules now protect Timber
Rattlesnakes in 12 counties of eastern and southern Iowa.

Jeff LeClere

Velvet Tails of the Blufflands: Field Observations 
and Anecdotal Information

Over 22 years, I have searched and searched, found timbers, not
found timbers, photographed more than several, molested many
gathering biological information, answered a few intriguing
questions, and pondered numerous riddles of Timber
Rattlesnake biology. Den areas are found in limestone and
dolomite outcrops, rookery sites in limestone and sandstone,
and summer pastures in hardwood forests and bluff prairies.
With others, I have documented egress and ingress dates, aver-
age and maximum sizes of males and females, color variation,
reproductive dynamics, maturity, longevity, frequency of shed-
ding, and behavior. Also during this time, the battle to remove
the Minnesota bounty was won, and the Timber Rattlesnake
was subsequently given legal protection in both Wisconsin and
Minnesota. However, in Minnesota, with this revived emphasis,
poaching and anti-rattlesnake sentiment have grown.

Seldom are rattlesnake bites to large animals such as cattle
and horses likely to be fatal, although facial and throat swelling
that restrict airways may be a concern. Dogs and rarely cats may
be bitten, most frequently in the head or front legs. Venomous
snakebite that produces rapid swelling and pain should be con-
sidered serious, and the animal should be taken immediately to
a veterinarian. The use of antivenin may be limited due to cost
factors, but aggressive medical therapy including antibiotics,
analgesics, and supportive therapy may be indicated.

A trio of male Timber Rattlesnakes at spring emergence. This site was destroyed by snake hunters later in the same season. Den rocks were dis-
lodged from the bluff, and several crushed Ringneck Snakes (Diadophis punctatus) were all that remained. The den has not been used since (Pierce
County, Wisconsin).

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The ultimate survival of “Velvet Tails” in the Upper
Mississippi River Valley must be about habitat protection, pub-
lic education, and a strictly enforced protective policy. Since
reestablishing dens is not a reliable option, attention should be
focused on known viable populations by providing relatively
large expanses of minimally managed habitat.

Barney Oldfield

The Ecology and Conservation of the 
Timber Rattlesnake in the 

Agricultural Landscape of Central Iowa
Since 2002, we have focused attention on a den site in Madison
County that appears to be healthy despite being adjacent to a
busy highway. Data are based on over 100 snakes plus litters
born in captivity from wild-caught females.

Monitoring about nine snakes implanted with radio trans-
mitters per year, we found that, in 2001, 42% of snake locations
were in edge/scrub habitats, 24% in woodland habitats, and 34%
in grassy/open habitats. Average canopy cover was 60%. Madison
County animals tended to have smaller home ranges and move
shorter distances than rattlesnakes in eastern populations.

An effort to document time spent in agricultural fields and
in natural versus disturbed habitats indicated that efforts aimed
only at protecting rock outcrops used as hibernacula are doomed
to failure if the entire range of the animals is not considered.
One individual, for example, spent nearly an entire season in a
field or along a fence line bordering a cow pasture. Much of the
remaining habitat in Iowa is extremely fragmented and
degraded, calling for conservation efforts on a landscape scale.

Jeffrey R. Parmelee and Paul W. Frese

Minnesota State Parks: Protecting Timber Rattlesnakes
within an Ecosystem Management Framework

The Minnesota Department of Natural Resource’s Division of
Parks and Recreation is legislatively mandated to preserve pre-
settlement natural features and communities as well as other nat-
ural, scenic, scientific, and historic features of significance. Given
this mandate, the Division has the responsibility to preserve and
perpetuate populations of Timber Rattlesnakes along with other
rare species.

The historic range of the Timber Rattlesnake in Minnesota
included eight southeastern counties that encompassed ten state
parks. The current range has decreased to six counties with seven
state parks. At least 37 historic den sites are known from those
seven parks. Assuming a minimum viable population size of
25–45 snakes per den suggests that these parks once supported
populations totaling about 1000–1600 individuals.

The bounty system in effect from 1909–1989 resulted in
these parks being heavily hunted. The impact of wanton killing
combined with vandalism of den sites and habitat degradation
due to disturbances have caused significant declines in popula-
tions (>90% in one park). Rattlesnakes have been extirpated in
three of the seven parks and populations in the other four have
declined dramatically. Only about one-third of historically active
den sites remain extant.

The Division’s objectives for these parks are: (1) To restore
or maintain native plant communities, and (2) to preserve or
restore animal populations so that all native species for which
reintroductions and maintenance are possible are present.
Specifically, for Timber Rattlesnakes, the objectives are: (1) To
restore sustainable populations to the three parks where the
species has been extirpated, and (2) To restore and maintain
existing populations at levels that are sustainable.

Since 2001, increased efforts to protect the species have
been funded through the State Wildlife Grant program, with
current work grouped into four main categories: Surveys and
monitoring, protection, habitat management, and education.

Ed Quinn and Shawn Fritcher

Habitat Selection and Home Ranges of Wisconsin 
Timber Rattlesnakes in the Mississippi River Valley

Data collected from nine radiolocated Timber Rattlesnakes 
(4 males, 3 females, 2 juveniles) and 353 subsequent observa-
tions (132 male, 129 female, 92 juvenile) reveal that all three
groups were found in secondary woodland more than expected
by chance (19% female, 24% male, and 39% juvenile versus
13% expected). The greatest disparity was for use of prairie habi-
tat (28% female, 2% male, 15% juvenile versus <2% expected).
Sumac/dogwood/blackberry shrub also was over-utilized (13%
female, 5% male, 11% juvenile versus <2% expected). Males
were found most frequently in mature oak woods (39%), but
less frequently than expected (43%). Males also utilized swamp
woodlands (24%) at about the expected rate (25%). Marsh (3%
female, 4% male, 0% juvenile versus 13% expected) and agri-
cultural habitats (0% female, 1% male, 0% juvenile versus 13%
expected) were under-utilized.

Richard A. Sajdak

36 IGUANA  •  VOLUME 13, NUMBER 1  •  MARCH 2006 TIMBER RATTLESNAKE SYMPOSIUM

A rust-colored middorsal stripe characterizes many Timber
Rattlesnakes from the Upper Mississippi River Valley (Pierce County,
Wisconsin).

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