Home Range, Site Fidelity, and Movements of the Timber Rattlesnake (Crotalus horridus) in West-Central Illinois

Abstract

Abstract Understanding the home range of reptiles is important to their conservation and recovery efforts. Despite numerous home range studies for the imperiled timber rattlesnake (Crotalus horridus), only a single study has been undertaken in the central midwestern United States. We report on the home range size, site fidelity, and movements of this species in west-central Illinois. Using VHF telemetry, we located 29 C. horridus (13 female, 16 male) every 1.3 days over a 5-year period for 51 years ofrecords of the species' locations and movements. We calculated annual home ranges for each snake per year using 99%, 95%, and 50% isopleths derived from Brownian Bridge utilization distributions, and we also report 100% minimum convex polygons for comparison with other studies. We examined the effects of sex, mass, SVL, and year on home range sizes and reportedon movement metrics as well as home range fidelity using both UDOI and BA statistics. The homerange sizes for male and non-gravid C. horridus were 56.91 Ha (CI = 41.04-72.77) and 20.22 (CI = 3.81-36.62) for 95% BBMM; 7.56 Ha (CI = 5.47-9.65) and 2.36 Ha (CI = 0.19-4.53) for 50% BBMM; and 80.03 Ha (CI = 50.95-109.11) and 30.80 Ha (CI = 1.55-60.06) for MCP. The estimated daily distance traveled was significantly greater for males (mean = 57.25 m/day, CI=49.06-65.43) than females (mean = 27.55 m/day, CI = 18.99-36.12). Similarly, maximum displacement distances from hibernacula were significantly greater for males (mean = 2.03 km, CI = 1.57-2.48) than females (mean = 1.29 km, CI = 0.85-1.73], and on average, males were located further from their hibernacula throughout the entirety of their active season. We calculated habitat fidelity using 11 snakes that were tracked over multiple years. The mean BBMM overlap using Bhattacharyya's Affinity (BA) for all snakes at the 99%, 95%, and 50% isopleths was 0.46 (SE=0.03), 0.38 (SE=0.03), and 0.08 (SE=0.02), respectively. The mean BBMM overlap for all snakes using the Utilization Distribution Overlap Index (UDOI) at the 99%, 95%, and 50% isopleths was 0.78 (SE=0.13), 0.41 (SE=0.03), and 0.09 (0.02), respectively. Our results are largely consistent with those of other studies in terms of home range sizes and theinfluence of sex on those home ranges and distances traveled. The species also exhibits strong site fidelity with snakes generally using the same habitats each summer. Particularly interesting was the tendency for snakes to disperse from specific hibernacula in the same general direction to the same general areas. We propose some possible reasons for this dispersal pattern.