The Biology of Rattlesnakes IIEdited by: Michael J. Dreslik • William K. Hayes • Steven J. Beaupre • Stephen P. Mackessy

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168 Dreslik et al. 2017

INTRODUCTION

Many organisms must move to satisfy their fundamental needs for food, reproduction, and survival (Turchin, 1998). Determining the intrinsic and extrinsic factors affecting why, when, where, and how animals move provides insight into how species interact with their environment to meet their needs (McLoughlin and Ferguson, 2000; Millspaugh and Marzluff, 2001). Such information ultimately provides a better understanding of a species’ biology; however, extrap-olation from one population to another is tenuous because species commonly show important biological differences across their ranges. Peripheral populations often differ ecologically from central populations and populations at latitudinal extremes frequently show variation in life history traits (Morrison and Hero, 2003; Blanck and Lamouroux, 2007; Sexton et al., 2009; Hardie and Hutchings, 2010).

Although spatial and temporal heterogeneity of resources may underlie the ecological differences among populations, linking such differences to specific environmental factors requires range-wide data (MacArthur, 1972; Wiens, 1976; Brown, 1984; Brown et al., 1995). Comparative studies of resource-oriented activities such as movement and space use can explain how environmental factors contribute to biological variation within species.

The Eastern Massasauga (Sistrurus catenatus) occurs in disjunct populations from western New York and southern Ontario to eastern Iowa and southwestern Illinois (Conant and Collins, 1998; Kubatko et al., 2011). Widespread decline over the past century has resulted in legal protection at the state/provincial level throughout its range (USFWS, 1998) and the species was subsequently listed as a candidate for federal listing under the U.S. Endangered Species Act of 1973 (USFWS, 1999). Recent findings of continued declines and chronic threats have led to the Eastern Massasauga being proposed as a threatened species in the United States (USFWS, 2015a,b). Because of the species’ conservation status, numerous studies on various aspects of its spatial biology have been conducted

Movement and Home Range of the Eastern Massasauga

(Sistrurus catenatus) at its Southern Range Limit

Michael J. Dreslik1,2, Donald B. Shepard1,3, Benjamin C. Jellen1,4, and Christopher A. Phillips1

1 Illinois Natural History Survey, Prairie Research Institute, University of Illinois Urbana-Champaign, Champaign, Illinois 61820, USA

ABSTRACT.—Studies of animal movement and space use provide insight into how species interact with their environment to meet food, reproductive, and survival needs. From March 2000 to November 2002, we used radio-telemetry to track the daily movements of 48 Eastern Massasaugas (Sistrurus catenatus) at the southern limit of the species’ distribution. Our goals were to determine if movement, home range, and activity area differed among sex and reproductive states and whether these variables were related to body size. We estimated movement parameters for 43 snakes and found individuals moved to new locations daily 63.2% of the time and moved an average of 12.3 m per day (SE = 1.0) and 20.8 m per move (SE = 1.5). We estimated home range sizes for 35 snakes. Average minimum convex polygon home-range size was 4.26 ha (SE = 0.95), 95% kernel density isopleths averaged 2.44 ha (SE = 0.20), and 50% kernel density isopleths averaged 0.33 ha (SE = 0.003). Neither movement parameters nor home range estimates differed among males, gravid females, and non-gravid females, nor did they vary with body size.

Dreslik, M. J., D. B. Shepard, B. C. Jellen, and C. A. Phillips. 2017. Movement and Home Range of the Eastern Massasauga (Sistrurus catenatus)

at its Southern Range Limit. Pp. 168–178 in Dreslik, M. J., W. K. Hayes, S. J. Beaupre, and S. P. Mackessy (eds.), The Biology of Rattlesnakes II.

ECO Herpetological Publishing and Distribution, Rodeo, New Mexico.

2 Correspondence e-mail: dreslik@illinois.edu3 Present address: School of Biological Sciences, Louisiana Tech

University, Ruston, Louisiana 71272, USA4 Present address: Urban Chestnut Brewing Company, St. Louis,

Missouri 63110, USA

Movement and Home Range of the Eastern Massasauga 169

throughout its distribution, including home range and movement (Table 1), habitat use (Wright, 1941; Mauger and Wilson, 1999; Harvey and Weatherhead, 2006a,b; Marshall et al., 2006; Moore and Gillingham, 2006), and relation-ships to roads (Shepard et al., 2008a,b; Rouse et al., 2011). The extensive body of research on S. catenatus has revealed ecological and life history variation across its range (Ernst and Ernst, 2003). Although studies have focused on the spatial ecology of S. catenatus near its northern range limit (Weatherhead and Prior, 1992; Johnson, 2000; Degregorio et al., 2011; Rouse et al., 2011), comparative data from the southern range limit of the species are lacking.

Here, we provide a detailed analysis of the spatial ecology of S. catenatus at its southern range limit in south-central Illi-nois. Such information will expand our knowledge of this broadly distributed species and will aid in understanding the environmental factors that contribute to the high degree of ecological variation among populations.

MATERIALS AND METHODS

Study area.—Carlyle Lake in southwestern Illinois is the largest man-made reservoir in the state with 10530 ha of surface water. Bordered by 4455 ha of state and federally managed lands, the reservoir’s major terrestrial habitats consist of upland and bottomland forest, old-field, and restored prairie within a larger agricultural matrix. Carlyle Lake is home to the largest known Illinois population of S. catenatus, which mainly occurs around the southern periphery of the lake.

Data collection.—We initially captured snakes through visual encounter surveys (Heyer et al. 1994) during spring egress (mid-March/April) and opportunistic encounters throughout the year. On capture, we classified snakes into one of three sex and reproductive states: non-gravid female, gravid female, or male. To determine sex, we probed the cloaca for hemipenal pockets or manually everted the hemipenes in males. To determine reproductive condition of females, we manually palpated them for the presence of enlarged follicles or used ultrasonography. Although females that were gravid in the spring would give birth later in the season, we retained their classification as gravid females for the entire active season to investigate potential differences in post-parturition behavior. For each snake, we measured snout-vent length (SVL) along the dorsal midline with a flexible tape to the nearest millimeter while the snake was restrained in a clear acrylic tube. SVL measurements were repeated until three were within 1 cm, then those three measurements were averaged. We measured mass with a Pesola® pull spring scale or an Ohaus® electronic balance to the nearest gram. We calculated a body condi-tion index for males and non-gravid females separately to

account for potential differences in sex from our long-term data set (snakes captured from 1999–present) by taking the residuals from the following non-linear equation Mass = aSVLb. Because body condition is a widely used measure accounting for both length and mass to assess individual health (Beaupre and Douglas, 2009), it could explain some of the variation observed in our analyses.

A subset of adult snakes >150 g in mass had tempera-ture-sensitive radio-transmitters surgically implanted by veterinarians at the St. Louis Zoological Park (HOLOHIL® Systems LTD, SI-2T – 9.3 g and SB-2T – 5 g), following the methods of (Reinert and Cundall, 1982). Transmitters were always <6% of the snake’s mass, and were typically <4%. After release, we located radio-implanted snakes daily between 0600–1900 h during the active season (from egress through ingress). To ensure that we located snakes at different times on consecutive days, we rotated tracking times between morning (0700–1059 hrs), mid-day (1100–1459 hrs), and evening (1500–1859 hrs). Once all snakes remained below ground for five consecutive days in the fall (inactive period), we reduced the intensity of tracking to once or twice weekly during the warmest part of the day.

Each time we located a snake, we recorded a GPS reading using a Garmin 12XL (NAD83 – UTM) and marked the site with a uniquely numbered flag. For each GPS reading we used the waypoint averaging function until the Estimated Position Error stabilized. Because atmospheric conditions, structural habitat, and satellite geometries affect GPS accu-racy, we took at least two readings per site (as described above) at least one week apart, assuming this would provide different satellite geometries and atmospheric conditions. If the two readings were within 5 m of each other, we averaged them. If not, we took successive readings under different satellite geometries and atmospheric conditions until two were within 5 m and averaged those readings. We considered that a snake had moved when successive loca-tions were >1 m apart (measured by a metric tape); thus, we did not consider minor changes in position or posture as moves.

Data analysis.—We conducted all spatial analyses in Arc-View® v3.2 using the Animal Movement Extension (Hooge and Eichenlaub, 1997) and BIOTAS® 1.02 beta (Ecological Software Solutions LLC). We analyzed all other data using the PopTools Excel add-in (Hood, 2010) and SPSS® 10.1 (SPSS Inc.), and set all nominal alpha levels at 0.05. When we violated the assumptions of normality, we transformed variables using either arcsine square root for proportions or natural logarithm for continuous variables. Based on bias analyses in Dreslik (2005), ≥30 radio-loca-tions/individual are required to allow meaningful inter-pretation of movement statistics. Therefore, we included only those snakes with ≥30 locations/year in movement

170 Dreslik et al. 2017

analyses. For space use, we used two forms of incremental area analysis (Hooge and Eichenlaub, 1997) to determine if a sample size bias existed in individual home range sizes. We used the Animal Movement extension in Arc-View® v3.2 (Hooge and Eichenlaub, 1997) for bootstrapped curves and BIOTAS® 1.03.2 alpha (Ecological Software Solutions LLC) for sequential curves. If either method indicated that an individual’s home-range size did not asymptote, then we omitted that individual from further analyses. Females that changed reproductive states (i.e., from gravid to non-gravid) between years were treated as different indi-viduals in the analyses because of the inherent biological differences in behavior, phenology, and activity.

We calculated the following movement parameters for each snake: mean distance moved per day, mean distance between consecutive unique locations, maximum distance between consecutive daily locations, total distance moved between the first and last location within an active season, and frequency of moves (number of detectable moves/days tracked). All distance measurements are straight-line distances taken once per day and are thus underestimates of the true movements of the snakes. We then constructed nine MANCOVA models with the five movement parame-ters as the dependent variables and different combinations of the main effect of sex and reproductive state and the covariates, number of radio-locations and body condition. We assessed which MANCOVA model best fit the data using an AIC approach (Burnham and Anderson, 1998). We used the number of radio-locations as a covariate to

account for potential sample size bias. For this analysis, the frequency of moves was arcsine square root transformed. We generated histograms of distance between consecutive locations for each sex and reproductive state to examine frequency distributions of moves in various distance classes.

Space use.—For each snake, we calculated four home range and activity area parameters: the minimum convex polygon (Mohr, 1947), the 50% and 95% kernel density isopleths (Worton, 1987, 1989, 1995; Seaman and Powell, 1996), and the number of activity centers. The minimum convex polygon (MCP) is a commonly used estimate of home-range size and allows comparison with other studies. However, MCPs do not provide information on differential intensity of space use and often include large areas that were not used. Kernel density isopleths (KDIs) do account for intensity of use, but are not as widely reported and are difficult to compare across studies due to variation in the smoothing parameter (h) used. Because they capture different aspects of space use, we refer to MCPs as home ranges and KDIs as activity areas. For KDIs, we used cross-validation of the smoothing parameter (h, Worton, 1989; Boulanger and White, 1990; Seaman and Powell, 1996). To allow comparison of KDI estimates of activity area among individuals, we standardized the smoothing parameter (h) by calculating the average h of all individual KDIs and then re-estimating KDIs for each individual using this h value. For individuals that were radio-tracked over multiple years, we averaged the home range param-

Table 1. Average minimum convex polygon (MCP) home-range size and mean daily distance moved per day (MDD) for Sistrurus catenatus across its range. Means are reported ±SE when possible; N is number of individuals on which statistics are based. †Study used repatriated individuals. ‡Populations in Missouri have been identified as Western Massasaugas, Sistrurus tergeminus (Gibbs and Chiucchi 2011; Kubatko et al. 2011), but are included here for historical reference and due to ecological similarities.

State MCP (ha) MDD (m) N SourcePennsylvania 0.98 ± 0.3 9.1 ±1.6 25 Reinert and Kodrich, 1982Michigan 1.3 ± 0.4 6.9 ± 1.1 16 Moore and Gillingham, 2006Pennsylvania 1.5 ± 0.4 3.7 ± 1.0 36 Kowalski, 2007Illinois 2.4 ± 0.4 13.5 ± 3.6 3 Wilson and Mauger, 1999Wisconsin 2.4 ± 1.6 ----- 10 Durbian et al., 2008Michigan 2.5 ± 5.7 11.8 ± 4.6 28 Bissell, 2006Indiana 4.0 10.5 26 Marshall et al., 2006Illinois 4.3 ± 1.0 12.3 ± 1.0 35 This studyWisconsin 6.6 9.8 32 King et al., 2004†

Missouri 7.4 ± 1.5 ----- 8 Durbian et al., 2008‡

Iowa 8.6 ± 2.0 15.5 ± 4.0 15 VanDeWalle, 2005Missouri 11.9 ± 3.8 ----- 10 Durbian et al., 2008‡

Michigan 16.7 ± 2.7 25.5 ± 2.2 58 DeGregorio et al., 2011Missouri 17.1 ± 4.3 ----- 27 Durbian et al., 2008, Seigel and Pilgrim, 2002‡

Ontario, Canada 25.0 ± 6.0 56.2 ± 12.4 11 Weatherhead and Prior, 1992New York 26.2 ± 4.5 19.5 ± 2.2 15 Johnson, 2000Wisconsin 135.8 ± 134.2 ----- 4 Durbian et al., 2008

Movement and Home Range of the Eastern Massasauga 171

eters across years. We then constructed nine MANCOVA models with the four home range and activity area param-eters as dependent variables and different combinations of the main effect of sex and reproductive states and the covariates, number of radio-locations and body condition. As above, model fit was assessed using an AIC approach (Burnham and Anderson, 1998).

RESULTS

From March 2000 to November 2002, we tracked the daily movements of 48 S. catenatus (21F:27M). Of these, we tracked 29 snakes for one year, 18 snakes for two consec-utive years, and one snake for all three years. By year, we tracked 16 snakes (6F:10M) in 2000, 24 (11F:13M) in 2001, and 27 (13F:14M) in 2002. The nonlinear equations for the relationship between mass and SVL (with standard errors in parentheses) was 0.008(0.003)∙SVL2.519(0.105)(r2 = 0.834, N = 349) for females and 0.002(0.001)∙SVL2.839(0.073)(r2 = 0.924, N = 345) for males.

Movements.—Forty-one snakes met the criteria of ≥30 radio-locations/year and two females switched repro-ductive state between years giving us a sample size of 43 individuals for movement analyses. Distance between successive locations followed a logarithmic distribution with movements of 0–5 m being the most frequent for all sex and reproductive states (Fig. 1).

When averaged by day, movements of non-gravid females were relatively consistent from late spring to early fall with minor oscillations during the summer (Fig. 2). In contrast, gravid females showed increased movement in mid-spring, decreasing movement through mid-summer, and then a sharp increase in late summer through early fall. Male movement peaked in the second half of the summer (Fig. 2). The best model included only the number of radio-loca-tions (Table 2). Models including sex and reproductive state

Figure 1. Histogram of the distances moved between successive radio-locations for 41 Sistrurus catenatus radio-located from spring 2000 to fall 2002 in southern Illinois. Movement is truncated to a maximum of 100 m because movements >100 m occurred at a low frequency. Two females changed reproductive condition during the study.

Figure 2. Five-day moving average distance moved per day for each sex/reproductive state in relation to time of year for 41 Sistrurus catenatus radio-located from spring 2000 to fall 2002 in southern Illinois. Two females changed reproductive condition during the study.

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172 Dreslik et al. 2017

and body condition had low support (Table 2). The overall MANCOVA for movement parameters was significant (Wilk’s λ = 0.036, F5,37 = 199.44, P < 0.001) when including the number of radio-locations as a covariate (Wilk’s λ = 0.107, F5,37 = 61.94, P < 0.001). For the 43 individuals with ≥30 radio-locations, the mean (±SE) daily distance moved was 12.3 ± 1.0 m, mean distance between moves was 20.8 ± 1.5 m, maximum distance moved averaged 163.6 ± 18.6 m, and total distance moved averaged 1,956 ± 269.3 m (Table 3). In addition, snakes changed locations, on average, 63.2 ± 0.2% of the time (Table 3).

Space use.—The tracking duration for snakes ranged from 58 to 597 days, yielding 51 to 535 locations per snake (mean = 154), of which 25 to 389 were unique points (Table 4). Based on incremental area analyses, we reduced our sample size to 33 individuals whose home range size estimates had stabilized; however, two of these were females that changed reproductive state between years, thus making our sample size for home range analyses 35. The best model included only the number of radio-locations whereas models including sex and reproductive state and body condition had low support (Table 2). The overall MANCOVA for home range and activity area parameters was significant (Wilk’s λ = 0.424, F4,30 = 10.17, P < 0.001), but the number of radio-locations was not a significant covariate (Wilk’s λ = 0.781, F4,30 = 2.10, P = 0.106). When corrected for the number of radio-locations, overall, home-range size aver-aged 4.26 ha for the MCP, 2.44 ha for the 95% KDI, and 0.33 ha for the 50% KDI (Table 4; Fig. 3). In addition, snakes had an average of two activity centers (Table 4).

DISCUSSION

Movement.—For S. catenatus in southern Illinois, emer-gence from hibernacula (egress) occurs from mid-March through April and entrance into hibernacula (ingress) occurs from mid-October to mid-November (Dreslik, 2005). Long-distance dispersal after emergence is prevalent among temperate-zone viperids (Landreth, 1973; Brown et al., 1982; Duvall, 1986; King and Duvall, 1990; Timmerman, 1995). For example, Crotalus viridis may move as much as 11 km (Duvall, 1986), C. horridus 1.4 km (Brown et al., 1982), and S. tergeminus edwardsii 3.4 km after emergence (Wastell and Mackessy, 2011). In some populations of S. catenatus, snakes disperse several hundred meters or more from their hibernacula (Weatherhead and Prior, 1992; King, 1999; Johnson, 2000; Marshall et al., 2006; Degregorio et al., 2011; Rouse et al., 2011), whereas snakes in other popu-lations remain within 200 m of their hibernacula (Reinert and Kodrich, 1982; Mauger and Wilson, 1999; Wilson and Mauger, 1999; Moore and Gillingham, 2006). Overall, we did not observe long-distance post-emergence dispersal; however, some snakes made long-distance moves (>200 m a day) when returning to hibernacula in the fall.

Males, gravid females, and non-gravid females showed temporal differences in movement across the active season. Movement in gravid females peaked in mid-spring, declined through mid-summer, and then peaked again in late summer and early fall. Parturition in S. catenatus in southern Illinois occurs in early August (Aldridge et al., 2008), thus gravid female movements early in the season

Figure 3. Example movement paths and home ranges for a gravid female, non-gravid female, and male Sistrurus catenatus from spring 2000 to fall 2002 in southern Illinois. Radio-locations, movement paths, minimum convex polygon (MCP), and 95% and 50% kernel density isopleths (KDI) are shown overlaid on maps of general habitat types.

Movement and Home Range of the Eastern Massasauga 173

Table 2. AIC results for the MANCOVAs on movement and home range parameters with K as the number of parameters in the model, Det. as the determinant of the pooled error sums of squares cross-product matrix divided by sample size, and Wi is the Akaike weight. For the models, N is the number of radio-locations, SS is sex/reproductive state, and BCI is the body condition index.

Movement Home Range and Activity AreasModel K Det. AIC ΔAIC Wi Model K Det. AIC ΔAIC Wi

N 38 23.75 -129.71 0.00 0.971 N 34.5 -2.81 -238.32 0.00 0.811SS+N+SS*N 43 23.54 -120.52 9.19 0.010 SS 34.5 -2.93 -235.13 3.19 0.165BCI+N 43 23.70 -119.91 9.81 0.007 BCI 34.5 -3.09 -231.25 7.07 0.024SS 38 26.39 -119.87 9.84 0.007 SRS+N 38.5 -3.14 -222.12 16.20 0.000BCI 38 26.57 -119.23 10.48 0.005 BCI+N 38.5 -3.25 -219.47 18.85 0.000SS+N+SS*N 48 23.36 -111.27 18.44 0.000 SRS+BCI 38.5 -3.37 -216.78 21.55 0.000BCI+N+BCI*N 48 23.53 -110.57 19.14 0.000 SRS+N+SRS*N 42.5 -3.17 -213.41 24.91 0.000SS+BCI 43 26.36 -109.96 19.75 0.000 BCI+N+BCI*N 42.5 -3.29 -210.62 27.70 0.000SS+BCI+SS*BCI 48 26.18 -100.60 29.12 0.000 SRS+BCI+SRS*BCI 42.5 -3.39 -208.21 30.11 0.000

Table 3. Raw and estimated marginal means (with standard errors) for the movement parameters of mean daily distance, mean distance between unique locations, maximum distance moved, and total distance moved (in meters), and the frequency of moves (%Moves) for 43 Sistrurus catenatus with ≥30 radio-locations tracked from spring 2000 to fall 2002 in southern Illinois. Frequency of moves was arcsin square root transformed for the analysis. The estimated marginal means from the MANCOVA account for the number of radio-locations (evaluated at 190.5).

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Non-Gravid Females (N =11) Mean 9.5 16.7 124.5 1307.4 59.9% 9.4 16.1 123.1 1393.6 59.4%SE 1.5 2.2 20.7 276.3 1.1% 2.0 3.1 36.4 350.0 1.0%

Gravid Females (N = 10) Mean 10.8 17.5 149.8 1403.7 58.9% 10.8 17.5 147.6 1378.3 59.2%SE 1.7 1.6 32.8 296.3 0.7% 2.1 3.1 37.0 355.8 1.0%

Males (N = 22) Mean 14.5 24.3 189.5 2531.3 66.8% 14.4 24.3 187.3 2452.9 66.9%SE 1.5 2.5 31.2 464.5 0.4% 1.4 2.1 24.9 240.0 0.5%

Overall (N = 43) Mean 12.3 20.8 163.6 1956.0 63.2% 12.3 20.8 163.6 1956.0 63.2%SE 1.0 1.5 18.6 269.3 0.2% 1.0 1.5 17.6 187.7 0.2%

Table 4. Raw and estimated marginal means (with standard errors) for the minimum convex polygon (MCP), 95% and 50% kernel density isopleths (in hectares), and number of activity centers (Cent.) for 35 Sistrurus catenatus with >30 radio-locations and home ranges attaining an asymptotic size tracked from spring 2000 to fall 2002 in southern Illinois. Also included are the means and standard errors (SE) for the duration of tracking (Dur.), the total number of radio-locations (Total), and the number of unique radio-locations (Uniq.). The estimated marginal means from the MANCOVA account for the number of radio-locations (evaluated at 164.5). Two females switched reproductive condition between years and each year was treated independently. The smoothing parameter h was 19.64.

Locations Raw Means Estimated Marginal MeansDur. Total Uniq. MCP 95% 50% Cent. MCP 95% 50% Cent.

Non-Gravid Females (N = 11) Mean 176 132 83 2.12 1.84 0.29 1.6 2.23 1.99 0.29 1.6SE 18 16 14 0.46 0.27 0.04 0.2 1.99 0.36 0.05 0.3

Gravid Females (N = 8) Mean 203 145 80 2.99 1.99 0.25 1.6 3.01 1.87 0.23 1.6SE 37 26 16 0.93 0.38 0.04 0.2 2.04 0.37 0.05 0.4

Males (N = 16) Mean 226 197 116 6.37 3.08 0.41 2.4 5.84 2.97 0.42 2.5SE 34 28 21 1.91 0.27 0.04 0.3 1.45 0.27 0.04 0.3

Overall (N = 35) Mean 205 164 97 4.26 2.44 0.33 2.0 4.26 2.44 0.33 2.0SE 19 16 11 0.95 0.20 0.03 0.2 0.92 0.19 0.03 0.2

174 Dreslik et al. 2017

are likely in search of gestation sites, decreased movement through mid-summer is likely associated with centering of activity around gestation sites, and post-parturition movements later in the season likely involve foraging to replenish lost energy reserves. Long-distance movements occur in gravid females of some snake species as they travel from over-wintering sites to gestation/oviposition sites (Parker and Brown, 1972; Madsen, 1984). In contrast, gravid female C. concolor (Ashton and Patton, 2001), C. viridis (Macartney, 1989), and C. oreganus (Gannon and Secoy, 1985) stayed relatively close to their den sites during gestation. Male movement was highest during the mating season in August and September and likely represents mate-searching (Jellen et al., 2007). Studies on C. cerastes (Secor, 1994), C. viridis (Duvall et al., 1985), C. scutulatus (Cardwell, 2008), C. mitchelli (Glaudas and Rodriguez-Ro-bles, 2011), and S. catenatus (Weatherhead and Prior, 1992; Marshall et al., 2006; Degregorio et al., 2011) found males increased movement during the mating season. In C. viridis, males that moved more frequently and in straighter paths had the highest mating success (Duvall and Schuett, 1997). Similarly, the number of females encountered by male S. catenatus was positively related to the distance moved during the mating season (Jellen et al., 2007).

Most studies on snakes have found greater variation in movement between gravid and non-gravid females than between males and females (Gregory et al., 1987). However, we found no difference in movement parameters between sexes and reproductive states. In Pennsylvania, S. catenatus, males and females also showed no difference in movement (Reinert and Kodrich, 1982) whereas in New York and Michigan gravid females moved less often and for shorter distances than males and non-gravid females (Johnson, 2000; Degregorio et al., 2011). We also found that all snakes moved at nearly the same frequency, ~60%. In the Bruce Peninsula of Ontario, S. catenatus also changed locations on average 60% of the time between tracking periods (Weath-erhead and Prior, 1992). In New York, male (72.2%) and non-gravid females (74%) changed locations with similar frequency, but gravid females changed locations only 45.5% of the time (Johnson, 2000).

Space use.—Home-range size estimates (MCPs) are avail-able for several populations across the range of S. catenatus (Table 1). Although variation in study duration, tracking frequency, and the number of individuals tracked compli-cates comparisons, our home-range estimates (average = 4.3 ha) fall in the middle of reported average sizes (Table 1). The largest reported home-range sizes for S. catenatus are from northern populations in Ontario, Canada (25.0 ha), Wisconsin (135.8 ha), and New York (26.2 ha; Table 1). Long-distance seasonal movements from overwintering sites in dense forested habitats to open habitats during the summer explain larger home ranges for the Bruce Penin-

sula, Ontario (Weatherhead and Prior, 1992; Harvey and Weatherhead, 2006b). Similarly, S. catenatus in New York made long-distance moves to and from hibernacula and summer foraging areas; however, they overwintered in a shrub-dominated peatland and moved to swamp and upland forest during the summer (Johnson, 2000). At southern latitudes where the climate is more moderate, S. catenatus typically overwinter and forage in the same habitat type, low and wet grasslands (Wright, 1941; Reinert and Kodrich, 1982; Mauger and Wilson, 1999; Dreslik, 2005; Moore and Gillingham, 2006; Kowalski, 2007). If sites where snakes can survive the winter become more limited with increased latitude (Harvey and Weatherhead, 2006a), then northern populations would be more likely to make long-distance seasonal migrations and have larger home ranges. Relaxed thermal constraints in southern latitudes could allow populations to forage and overwinter in or near the same area, reducing the need for long-distance migrations and resulting in smaller home ranges. Our study population is located at the southern periphery of the range of S. catenatus, yet our home-range size and move-ment distances fall in the middle in comparison to other populations (Table 1). Thus, although there is a trend for more northern populations to have larger home ranges and move greater distances, factors specific to each population also contribute to the variation observed across the species’ distribution.

Habitat heterogeneity and fragmentation may also explain inter-population variation in home-range size. Eastern Diamondback Rattlesnakes (Crotalus adamanteus) had smaller home ranges in highly heterogeneous habitats (Hoss et al., 2010) and Eastern Indigo Snakes (Drymarchon couperi) had smaller home ranges in fragmented habitats (Breininger et al., 2011). Roads, in particular, may constrain movements and result in smaller home ranges if snakes actively avoid crossing them (Andrews and Gibbons, 2005; Andrews et al., 2008). Shepard et al. (2008b) showed that S. catenatus at our study site crossed roads less often than expected and experienced high mortality during road crossing attempts (Shepard et al., 2008a). If this selects for decreased movement and road avoidance, then the contemporary and historical effects of roads may reduce home-range sizes in some S. catenatus populations.

Space use can vary with body size, sex, and reproductive condition because of differences in underlying resource and reproductive requirements. For example, if large snakes consume larger prey and large prey require larger areas, then larger snakes should also have larger activity areas (Macartney et al., 1988). In viperids, gravid females must gestate offspring and the need for suitable thermo-regulation sites throughout the gestation period may result in decreased movement and reduced activity area. Further, male viperids typically increase movement during the

Movement and Home Range of the Eastern Massasauga 175

mating season as they search for females, which may result in them having larger activity areas (Jellen et al., 2007; Glaudas and Rodriguez-Robles, 2011). Contrary to our expectations, we found no overall difference in home range and activity area estimators among sex and reproductive states, similar to a study on S. catenatus in western Pennsyl-vania (Reinert and Kodrich, 1982). Two additional studies showed that male S. catenatus had larger home ranges than both gravid and non-gravid females (Marshall et al., 2006; Degregorio et al., 2011). The lack of significant differences in home-range and activity-area sizes in our study may reflect relaxed thermal constraints on gestation in gravid females and/or a barrier effect of roads, which would constrain home range and activity areas most severely in males.

Conservation implications.—Most movements of S. catenatus in southern Illinois were short, but times when snakes make more long-distance moves expose them to increased risk of mortality from both natural and anthro-pogenic causes (Bonnet et al., 1999). Therefore, conserva-tion actions aimed at increasing the area of suitable habitat should consider the removal or reduction of potential barriers that may impede movement or contribute to mortality. The home-range and activity-area sizes of S. catenatus in this study were similar to those found in other studies across the species’ range, and most individuals had one or two centers of activity. If we conservatively assume that a snake needs a minimum 0.33 ha of temporally discrete habitat, we could estimate a hypothetical carrying capacity (K) per site. In 2005, there were roughly 176 ha of fragmented and disjunct habitat for S. catenatus at our study site with parcels averaging 5.3 ha (Dreslik, 2005). Using our estimate of 0.33 ha per snake, and assuming no overlap in 50% KDI’s, this translates to a current regional K of 533 individuals with parcels averaging 16 individuals. As an example, one of our sites, South Shore State Park, has 20.3 ha of suitable habitat, which equates to a K of 62 indi-viduals. The average population size at this study site based on 12 years of mark-recapture data was estimated to be 54 snakes using a closed population estimator on the spring emergence population size (Dreslik et al., this volume). This is close to the estimated K of 62 individuals obtained using the 50% KDI estimation method. The congruence between these two measures suggests that we could use our 50% KDI area to estimate the habitat required to achieve a specific population size. For example, at our study site a population of 500 snakes would require 165 ha of suitable habitat. Durbian et al. (2008) recommended that 100 ha should be the minimal target area for sustaining a popu-lation of S. catenatus; using our method, 100 ha of suitable habitat at our study site would support 303 individuals. Unfortunately, the number of individuals that constitute a minimum viable population of S. catenatus is unknown, but our results appear to provide a general estimate of how

much habitat would be required and afford a numerical target for land management agencies.

ACKNOWLEDGEMENTS

We thank J. Bunnell, J. Birdsell, G. Tatham, J. Smothers, D. Baum, and other personnel in the U.S. Army Corps of Engineers and Illinois Department of Natural Resources for field assistance and logistical support. We thank A. Kuhns, P. Jellen, J. Mui, J. Petzing, B. Heinhold, T. Anton, D. Mauger, S. Ballard for assistance in the field conducting radiotelemetry. We thank Dr. Randy Junge and the St. Louis Zoological Park for graciously donating their time, facilities, surgical expertise, and general veterinary care. The Illinois Department of Natural Resources, U.S. Fish and Wildlife Service, Illinois Wildlife Preservation Fund, and U.S. Army Corps of Engineers provided financial support. All animals in this study received humane treatment adhering to the “Guidelines for Use of Live Amphibians and Reptiles in Field Research” published by Society for the Study of Amphibians and Reptiles, American Society of Ichthyolo-gists and Herpetologists, and Herpetologists’ League. We conducted this study in accordance under the University of Illinois IACUC protocol #08019 and Illinois Department of Natural Resources T&E species permit #05-11S.

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