Journal of Herpetology, Vol. 41, No. 3, pp. 451–457, 2007
Copyright 2007 Society for the Study of Amphibians and Reptiles
Male Movement and Body Size Affect Mate Acquisition in the Eastern
Massasauga (Sistrurus catenatus)
BENJAMIN C. JELLEN,1 DONALD B. SHEPARD,2 MICHAEL J. DRESLIK,
AND
CHRISTOPHER A. PHILLIPS
Illinois Natural History Survey, Center for Biodiversity, 1816 South Oak Street, Champaign, Illinois 61820, USA
ABSTRACT.—Knowledge of mating system characteristics can elucidate forces driving sexual selection. In
male pitvipers, both male movement tactics and body size are predicted to be important determinants of
reproductive success. We used radio telemetry to monitor free-ranging Sistrurus catenatus (Eastern
Massasauga) from 2000 through 2002 to determine whether male movement tactics and body size affect
mate acquisition. Reproductive behaviors peaked in late July to early August. Females were accompanied by
multiple males per season (up to seven); however, male mate acquisition varied considerably with only three
of 17 (18%) males located more than one female during a single mating season. During the mating season,
male mean daily distance moved (21.8 m) and movement frequency (77%) were higher than during the
nonmating season (13.3 m, 63%). Male movement rate and body mass were positively related to the number
of females acquired, and heavier males were observed accompanying females as the mating season
progressed. Our results indicate that both movement tactics and body size are important in the mating
system of S. catenatus; however, direct measures of reproductive success will be necessary before assessing
the intensity of sexual selection.
Knowledge of mating system characteristics
can elucidate forces driving sexual selection
(Darwin, 1871; Shine, 1978; Duvall et al., 1993).
In many species, males compete for females,
a limited resource (Bateman, 1948; Emlen and
Oring, 1977; Parker, 1984), through direct (malemale agonistic behavior) and indirect (mate
locating ability) means, and variation in reproductive success leads to selection for those
traits that enhance fitness (Darwin, 1871; Andersson, 1994). Most of the empirical data that
have formed the basis of sexual selection and
mating system theory have come from a limited
group of organisms (Thornhill and Alcock, 1983;
Andersson, 1994; Shuster and Wade, 2003). New
insights into these areas are likely to be provided
by studies on other, often overlooked, taxa. With
technological advances in methodology (e.g.,
radio telemetry), snakes have become increasingly accessible subjects in predictive behavioral
studies, and their lack of ornamentation, parental
care, and social bonds make them ideal candidates for such studies (Schuett, 1997; Shine and
Bonnet, 2000; Prosser et al., 2002).
Despite recent attention, mating systems remain among the most poorly understood
1
Corresponding Author. Present address: Department of Biology, Saint Louis University, 3507 Laclede
Avenue, Saint Louis, Missouri 63103, USA; E-mail:
[email protected]
2
Present address: Department of Zoology and Sam
Noble Oklahoma Museum of Natural History, University of Oklahoma, 2401 Chautauqua Avenue,
Norman, Oklahoma 73072, USA
aspects of snake ecology, although some generalities have emerged. For example, the mating
system of most viperid snake species appears to
fall along a continuum between two mating
system extremes: Prolonged Mate Searching
Polygyny (PMSP) and Female Defense Polygyny (FDP). In species that exhibit PMSP, such as
the Western Rattlesnake (Crotalus viridis), receptive females are wide-ranging and spatially
unpredictable during the mating season. Therefore, males must make long movements in
search of females, male-male agonistic encounters are infrequent, and combat is virtually
absent from the mating system (Duvall et al.,
1992, 1993). At the other extreme are species that
exhibit FDP, such as the European Adder
(Vipera berus). Under this mating system, receptive females are clustered and spatially
predictable during the mating season allowing
males to guard and defend one or more females
from conspecific males. This spatial distribution
makes male-male agonistic encounters frequent,
and male movement during the mating season
is restricted to the immediate vicinity of the
female(s) (Duvall et al., 1992, 1993; Madsen et
al., 1993).
The mating systems of many terrestrial snake
species, particularly viperids, are predicted to
have characteristics of both systems (Duvall et
al., 1992, 1993), and factors influencing male
reproductive success will vary depending on
where the mating system lies along the PMSP/
FDP continuum. On the PMSP extreme, male
movement during the mating season should be
the major determinant of reproductive success,
452
B. C. JELLEN ET AL.
whereas fighting ability (i.e., body size) should
be the major determinant on the FDP extreme.
Mating systems that fall in the middle should
have characteristics of both, with the relative
importance of male movement and body size
varying with social structure and resource
distribution (i.e., receptive females; Shine,
2003). This theoretical framework allows us to
generate predictions concerning the relationships between mate acquisition, movement, and
body size in male viperids. First, if receptive
females are wide-ranging during the mating
season, then we predict that male movement
(mean daily distance moved and movement
frequency) will be higher during the mating
season than during the nonmating season.
Second, male movement rate will be a good
predictor of whether a female is located and will
be positively related to the number of females
located. Third, because larger males typically
win agonistic encounters against smaller males
(Schuett, 1997), we predict that larger males will
accompany more females. Here, we test the
above predictions by examining the factors
influencing male mate acquisition in the mating
system of the pitviper Sistrurus catenatus (Eastern Massasauga). The mating system of S.
catenatus provides an ideal system to test these
predictions because it contains characteristics of
both PMSP (wide-ranging receptive females;
Dreslik, 2005) and FDP (male-male agonistic
behavior; Shepard et al., 2003; Mauger and
Wilson, 2005; VanDeWalle, 2005). Further, females experience a biennial reproductive cycle
(Aldridge et al., in press) thereby intensifying
male intrasexual selection pressures (i.e., malebiased operative sex ratio; Emlen and Oring,
1977).
MATERIALS AND METHODS
Study Sites.—This study occurred along the
southern periphery of Carlyle Lake, Clinton
County, Illinois within Illinois Department of
Natural Resources and U.S. Army Corps of
Engineers managed properties. Study sites were
comprised mainly of fallow grasslands with
a patchy forb distribution and adjacent floodplain forest or savanna.
General Methodology.—During spring egress
from 2000 through 2002, we located snakes
through visual surveys at potential and known
hibernacula. We also included snakes incidentally encountered throughout the season. Individuals were sexed by cloacal probing for the
presence of hemipenal pockets (Schaefer, 1934).
With the individual secured in a tube, we
measured snout–vent length (SVL) to the
nearest centimeter by averaging three repeated
measurements with a flexible tape that were
within 1 cm, and mass to the nearest gram with
pull spring scales or an electronic balance.
Snakes with a SVL greater than or equal to the
SVL of the smallest individual exhibiting reproductive behaviors (46 cm) were classified as
adults. Our criterion was similar to other
reports of minimum adult SVL: 44.8 cm (Pennsylvania; Reinert, 1981) and 50.1 cm (Missouri;
Seigel, 1986). We individually marked adults by
clipping ventral scales (modified from Brown
and Parker, 1976), injecting passive integrated
transponder tags subcutaneously, and painting
rattle segments with nail polish. The latter
method allowed identification from a distance
without disrupting the snake’s behavior.
Radio transmitters were surgically implanted
by St. Louis Zoological Park veterinarians at the
park’s animal hospital and generally followed
Reinert and Cundall (1982). We used HOLOHIL
Systems SI-2T, 8.9-g and SB-2T, 5.2-g and AVM
Instrument Company SM1-H, 9.0-g transmitters
that were allotted such that they accounted for
less than 6% of the snake’s body mass. We
monitored all radio-equipped snakes, regardless of reproductive condition, for reproductive
behaviors once daily throughout the active
seasons (generally early April through midNovember). Monitoring time was rotated between morning, afternoon, and evening on
a daily basis to observe snakes during all
daylight hours (0600–2100). To minimize disturbance, snakes were observed for no more
than 3 min per daily encounter. At each snake
location, we recorded an initial GPS reading
(NAD 83–UTM) and marked it with a uniquely
numbered flag. GPS coordinates were measured
using a Garmin GPS 12 series unit with
waypoint averaging; accuracy averaged 6
4 m. Movements ,1 m were not considered
unique locations and were given the same
coordinates. For movements .1 m, we recorded
a second GPS reading on a subsequent day
(under different satellite geometry) and averaged the two coordinates if they were within
5 m of one another. If the coordinates were not
within 5 m of one another, we took additional
readings under different satellite geometries
until at least two points were within 5 m. In
2000, we remeasured and reweighed radioequipped snakes monthly to obtain accurate
size data during the mating season. After 2000,
to minimize disturbance and because monthly
changes were negligible, we remeasured and
reweighed snakes only once per season, shortly
before we expected the mating season to
commence based on data from the 2000 mating
season.
A reproductive behavior was scored for each
daily observation of a male-female paring and
was initially classified into the mutually exclu-
MASSASAUGA MATING SYSTEM
sive categories of (1) proximity, adult malefemale pairs were within 1 m but not touching;
(2) contact, bodies of adult male-female pairs
were touching but not copulating; and (3)
copulation, the adult male-female pair were in
coitus. In 2001, we further subdivided the
contact category into simple contact (no courtship behaviors observed) and courting (courtship behaviors such as body flexions, chin
rubbing, and tail looping [Chiszar et al., 1976;
Shepard et al., 2003]). We also classified a snake
as mate-searching when it was observed moving, tongue flicking rapidly, and probing the
substrate with its head; and we could confirm
that an adult of the opposite sex was, or had
recently been, in the immediate vicinity. Because only adult male-female pairs exhibited
these behaviors, and these behaviors were
consistent with previous observations of mating
S. catenatus in captivity (Chiszar et al., 1976), we
assumed these categories represented behaviors
associated with reproduction. We considered
the mating season to have commenced with the
first observation of a reproductive behavior and
concluded with the last observation for the
season. Because a distinct mating season was
not evident in 2002 (discussed below), it was
estimated using the earliest and latest dates
a reproductive behavior was observed from the
two previous seasons.
Data Analysis.—Distance moved per day was
calculated from GPS coordinates of a snake’s
daily location throughout the season. To determine whether male mean daily movement
and movement frequency were greater during
the mating season than during the non-mating
season, we used a paired t-test and a Wilcoxon
signed-rank paired sample test respectively
(one-tailed probability because of an a priori
hypothesis concerning the direction of the
difference). We used logistic regression to
determine whether male mean daily movement
rate during the mating season was a good
predictor of whether a female was located. We
used linear regression to test whether male
movement rate during the mating season was
positively related to the number of females
located. To test whether male body size was
positively related to the number of females
located, we used linear regressions of SVL and
mass versus the number of females located. We
also used linear regression to test whether male
size (SVL and mass) was related to movement
rate. To test whether a temporal pattern existed
in the size of males accompanying females (i.e.,
increasing or decreasing size as the mating
season progressed), we subdivided the mating
season into seven-day periods, averaged the
SVL and mass of all males observed accompa-
453
nying females during each period and then
regressed SVL and mass against time period.
All data were analyzed using Microsoft
ExcelH, SPSSH, and SYSTATH. We log-transformed all distance and size variables prior to
analyses to meet assumptions of normality and
homogeneity of variances. All means are reported 6 1 SD, and the nominal alpha level was
set a priori at 0.05. No differences existed
among years for any movement or size variable
(results not presented); thus, we pooled data
across years. We used one-tailed probabilities
only in two cases when the a priori hypotheses
involved specific predictions about the direction
of the difference (i.e., because of PMSP, male
mean daily distance moved and movement
frequency are predicted to be higher during
the mating season than during the nonmating
season).
RESULTS
Mating Season Phenology.—We observed 128
instances of reproductive behavior (77 contact,
37 proximity, 11 copulating, and 3 searching) involving 46 unique male-female pairings (Table
1). Reproductive behaviors were observed predominantly from the fourth week of July
through the fourth week of September, peaking
in late August to early September. The only
observation of reproductive behavior outside
this period occurred on 16 April 2002 when we
observed a male-female pair exhibiting contact
behavior. Three of 46 (7%) pairings were of
males accompanying postpartum or gravid
females.
Male Movement.—On average, males made
longer (t16 5 3.21, Pone-tailed 5 0.0025; Table 2)
and more frequent (Z 5 3.01, N 5 17, Pone-tailed 5
0.0015; Table 2) daily movements during the
mating season than during the nonmating
season. Further, the mean daily distance a male
moved during the mating season was a good
predictor of whether he located a female (B 5
3.96, x21 5 4.00, P 5 0.045), and the number of
females located was positively related to the
mean daily distance moved (R2 5 0.66, F1,15 5
29.0, P , 0.001).
Male Size.—Within a given mating season,
nongravid females (N 5 10) paired with a mean
of 3.5 6 2.4 males (range 1–7) for an average of
2.8 6 1.7 days (range 1–12) per male. Although
the number of unique pairings decreased in
2001 (t8 5 5.03, P 5 0.001; Table 1), the time
spent in pairings was the same for both years (t7
5 0.59, P 5 0.58). Males located a mean of 0.82
6 1.38 females (range 0–5; N 5 17) per mating
season, but female acquisition varied considerably. The majority of males located no females,
and only a few males located multiple females
454
B. C. JELLEN ET AL.
TABLE 1. Number of radio-equipped Sistrurus catenatus during the mating season, number of unique malefemale pairings observed, and number and type of observed reproductive behaviors exhibited from 2000–2002
at Carlyle Lake, Clinton County, Illinois.
Year
# snakes
tracked
# unique
pairings
Proximity
Contact
Courting
Copulating
Searching
Total # rep.
bhvr
2000
2001
2002
Total
5F, 5M
8F, 7M
8F, 5M
21F, 17M
25
19
2
46
20
17
0
37
35
33
2
70
NA
7
0
7
8
3
0
11
NA
3
0
3
63
63
2
128
(Table 2). Male SVL was not related to the
number of females located (R2 5 0.05, F1,15 5
0.78, P 5 0.39), but male mass was positively
related (R2 5 0.33, F1,15 5 7.23, P 5 0.017).
Neither male SVL (R2 5 0.003, F1,15 5 0.05, P 5
0.83) nor mass (R2 5 0.15, F1,15 5 2.64, P 5 0.13)
were related to movement rate during the
mating season; thus, significant results for body
size were not caused by larger males simply
moving more. As the mating season progressed,
heavier males were observed accompanying
females (R2 5 0.33, F1,15 5 7.31, P 5 0.016),
but no trend was evident for male SVL (R2 5
0.05, F1,15 5 0.80, P 5 0.38).
DISCUSSION
Mating Season Phenology.—Almost all (99.2 %)
of the reproductive behaviors observed during
the three-year study period occurred between
24 July and 22 September. The timing of the
mating season of S. catenatus at Carlyle Lake is
consistent with reports from Pennsylvania (Reinert, 1981) and New York (Johnson, 2000). Reproductive behaviors exhibited by temperatezone pitvipers during the spring are hypothesized to be an artifact of the ancestral mating
season observed in the tropics, which, in the
temperate zone, has been interrupted by winter
(Aldridge and Duvall, 2002).
Ectothermic vertebrates are predominantly
iteroparous animals with asynchronous reproductive cycles and low frequencies of reproduction (Bull and Shine, 1979). Because of the
extreme costs associated with reproduction,
adult female pitvipers mate only when they
have sufficient energy reserves (Shine, 1980;
Aldridge and Duvall, 2002) and these limitations usually result in a biennial or longer
female reproductive cycle (Bull and Shine,
TABLE 2. Snout–vent length (SVL, cm), mass (g), mean daily distance (m) moved and movement frequency
(%) during the nonmating and mating seasons 6 1 SD, number of radiolocations (N) for which statistics are
based, and number of females located for successful and unsuccessful radio-equipped male Sistrurus catenatus
from 2000–2002 at Carlyle Lake, Clinton County, Illinois.
Nonmating season
Male #
186
51
111
81
151
182
245
Successful Avg.
34
39
68
76
95
96
137
270
303
317
Unscsfl. Avg.
GRAND Avg.
SVL
(cm)
Mass
(g)
68.1
59.8
66.9
49.7
70.0
57.3
66.7
62.6
50.0
57.0
55.0
57.6
65.3
58.2
72.0
64.3
70.6
60.0
61.0
61.7
426
365
391
130
426
208
315
323
152
165
188
231
257
172
340
217
301
222
225
265
Avg. daily dist.
moved (m)
32.7
13.4
32.4
7.5
11.5
9.9
4.2
15.9
10.9
22.6
10.6
13.5
8.6
11.0
11.6
13.2
5.9
6.4
11.4
13.3
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
57.0
17.6
81.8
8.8
22.7
23.3
7.6
31.3
7.8
21.0
9.1
25.0
24.6
28.3
18.7
32.1
11.3
13.8
19.2
31.6
Mvmnt.
freq.
77
78
68
64
56
45
43
62
100
100
93
83
37
40
64
43
46
38
64
63
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
42
42
47
49
50
50
50
47
0
0
26
38
49
49
48
50
50
49
36
22
Mating season
N
99
49
79
42
107
96
55
75
62
60
68
99
108
120
125
128
123
115
100
90
Avg. daily dist.
moved (m)
57.7
53.1
45.0
25.0
15.8
17.8
19.9
33.5
8.7
11.7
15.3
22.9
8.5
25.2
10.8
15.7
10.1
7.4
13.6
21.8
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
93.6
70.4
102.8
39.3
30.3
27.6
30.4
56.3
6.3
9.3
15.1
34.1
17.0
67.0
13.2
28.7
14.8
13.8
21.9
15.6
Mvmnt.
freq.
77
100
70
100
60
69
91
81
97
100
100
98
48
52
58
69
68
43
73
77
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
43
0
46
0
50
47
30
31
17
0
0
14
50
50
50
46
47
50
32
20
N
# RR Located
43
19
43
47
43
42
11
35
35
22
49
53
60
60
43
59
59
60
50
44
5
3
2
1
1
1
1
2
0
0
0
0
0
0
0
0
0
0
0
0.8
MASSASAUGA MATING SYSTEM
1979). Female S. catenatus at Carlyle Lake
reproduce predominantly biennially (Aldridge
et al., in press) and, perhaps, somewhat synchronously. Only two instances of reproductive
behavior were observed in 2002. During the
spring of 2002, Carlyle Lake suffered its worst
flooding event since the dam’s inception in
1967, and portions of the site were inundated
for up to four weeks. Floods have been previously implicated in altering reproductive
cycles in S. catenatus (Keenlyne, 1978; Seigel et
al., 1998), possibly through habitat alteration
and the impact on prey availability; but direct
evidence is lacking and the effect on reproduction remains unknown.
Females generally do not mate immediately
following parturition because of depleted energy
reserves (for review, see Aldridge and Duvall,
2002) and males typically do not engage in
reproductive behaviors with nonreproductive
females (Rahn, 1942; Brown, 1995; Naulleau et
al., 1999). We observed two instances of males
exhibiting reproductive behaviors with postpartum females and one instance of a male exhibiting reproductive behavior with a gravid female.
Because female S. catenatus are wide-ranging
during the mating season (Dreslik, 2005), the
occurrence of long-term sperm storage (Schuett,
1992), and the relatively low cost of sperm
(Bateman, 1948; Trivers, 1972), insemination of
any female encountered (regardless of her reproductive condition) during the mating season
might be an advantageous strategy. However,
nonreproductive females may not be receptive to
male sexual advances, and it is unknown
whether male viperids can force copulations
such as male Thamnophis sirtalis have been
reported to do (Shine et al., 2003).
Male Movement.—When receptive females are
wide-ranging and spatially unpredictable, mate
searching tactics will determine male reproductive success (Duvall et al., 1992, 1993; Shine,
2003). In our study, male mean daily distance
moved and movement frequency increased
during the mating season, and the distance
a male moved was directly related to his female
location success. Our results are consistent with
other viperids, such as C. viridis (Duvall and
Schuett, 1997), C. horridus (Brown, 1995), and V.
berus (Madsen et al., 1993), in which more vagile
males located females more frequently compared to more sedentary males. However,
simply moving more may not be the only
determinant of success in locating females, as
the movement path may also be important. For
example, male C. viridis that moved in straightline paths had the most success in locating
females (Duvall and Schuett, 1997). We did not
analyze movement path in our study, but doing
so might explain some of the additional
455
variation in mate acquisition success among
males.
In species where males compete for females,
the intensity of sexual selection is largely
influenced by the variance in male reproductive
success (Andersson, 1994). In species under
strong intrasexual selection, a small number of
males obtain the majority of the matings. This
appears to be exactly the case in our study where
most males acquired zero or one female and only
three males acquired multiple females (range 2–
5; Table 2). Most males did not move large
distances, and most did not acquire mates, but
this should not be unexpected because increased
movement is associated with increased risks
such as exposure to predators (Klauber, 1972),
increased energy usage (Bonnet and Naulleau,
1996), reduced food intake (Martin, 1992), and
increased anthropogenic mortality (Aldridge
and Brown, 1995; Bonnet et al., 1999). In our
study area, road mortality of S. catenatus was
highest during the mating season and consisted
primarily of adult males (DBS, unpubl. data).
Although a high movement rate resulted in
multiple females for a few males during the
mating seasons under study, it is unknown how
differing strategies of low versus high movement
affect lifetime reproductive success.
Male Size.—The sex ratio in many pitviper
populations is biased toward males, which are
capable of reproducing annually (Klauber, 1936;
Fitch, 1960). When this is coupled with the
biennial or longer female reproductive cycle
(such as S. catenatus at Carlyle Lake), the
operational sex ratio (OSR) in a given season
is strongly male-biased intensifying intrasexual
competition for mates (Emlen and Oring, 1977).
As a consequence, ritualized male combat is
prevalent in many North American pitviper
species (Shine, 1978; Carpenter, 1986). When
receptive females are clustered, larger males
have higher reproductive success because they
typically win agonistic encounters against
smaller males (Schuett, 1997). In our study,
longer males did not accompany more females,
but heavier males did. Because male body size
was related to mating success, theory predicts
that male agonistic encounters should be frequent. However, during the three-year investigation, we observed only one aggressive interaction between males (Shepard et al., 2003).
Male combat was also rare in C. viridis;
however, body size was not related to mating
success in this species (Duvall and Schuett,
1997). Although female S. catenatus are spatially
unpredictable during the mating season, the
limited observations of combat in this study
were likely caused by the little opportunity we
had to observe intrasexual interactions (approximately 3 min per daily encounter). Additional
456
B. C. JELLEN ET AL.
observation during the mating season may
reveal that male-male agonistic interactions
occur more frequently. The increasing size
(mass) of males accompanying females as the
mating season progressed also indicates that
body size is important in male-male interactions
and mate acquisition. This pattern could be
related to timing of female peak receptivity and
indicative of mating order effects.
Mating System.—Because both movement and
body size influence male reproductive success,
the mating system of S. catenatus falls between
PMSP and FDP. In snakes, the ability to
encounter females is related to mate searching
tactics, whereas the ability to defend or steal
them once encountered depends on male fighting ability (Shine, 2003). Once a female is located,
male S. catenatus typically coil their bodies
around and on top of the female, court her, and
will respond aggressively if approached by
intruding males (Shepard et al., 2003; Mauger
and Wilson, 2005; VanDeWalle, 2005). Male S.
catenatus usually accompany females for multiple days, and it is likely that other males are
attracted to the area around the female by
pheromonal cues. During this period, male size
would play an important role in defending or
stealing the female from another male, because
size has been shown to be a major determinant of
fighting success (Luiselli, 1995; Schuett, 1997).
Ultimately, the relative importance of male
movement and size will depend on the temporal
and spatial distribution of receptive females,
which vary within and among seasons and
populations (Madsen and Shine, 1992; Shine,
2003). Males should adjust their mating tactics
accordingly to maximize reproductive success.
Snakes, pitvipers in particular, afford abundant opportunities to study sexual selection and
mating systems. In most studies thus far, male
reproductive success has been estimated by the
number of females acquired, and it was unknown whether males actually inseminated
every female and sired offspring. The number
of females a male pitviper acquires is likely
correlated with his reproductive success, but
this could be untrue if sperm competition
(Parker, 1984) and cryptic female choice are
present. New insights from paternity analysis
would provide a more accurate picture of the
mating system (e.g., Weatherhead et al., 2002)
and help elucidate the relative importance of
movement tactics and body size in determining
male reproductive success. We provide evidence that both movement tactics and body size
are important in the mating system of S.
catenatus, but direct measures of reproductive
success will be necessary before assessing the
intensity of sexual selection (Duvall et al., 1993).
Acknowledgments.—Research was conducted in
accordance with all University of Illinois Institutional Animal Care and Use Committee
guidelines and under appropriate permits from
the Illinois Department of Natural Resources.
Funding for this project was made available
through grants from the Illinois Department of
Natural Resources (IDNR) and U.S. Fish and
Wildlife Service. We wish to thank the St. Louis
Zoological Park for performing implantation
surgeries and providing for the general health of
the snakes. We also thank the IDNR and ACE for
their cooperation and assistance. Finally, we wish
to thank everyone who assisted us in the field.
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Accepted: 4 April 2007.