Increasing Body Size after Exploitation in a Population of Timber Rattlesnakes (Crotalus horridus)
At a field site in northeastern New York during a 40-yr study, we measured the body sizes (total length, snout–vent length [SVL], mass) in three intrinsic groups of adult Crotalus horridus: nongravid (N) females, gravid (G) females, and males. We argue that a bounty system in effect for 75 yr caused a probable decline of the largest animals. After this lengthy period of exploitation, we observed that body sizes began to increase. Across 4 decades, the three intrinsic groups were significantly larger in the final decade (2009–18) than in the first decade (1979–88), stabilizing at a mean body mass of ≈710 g in N females, ≈870 g in G females, and ≈1,200 g in males. Mean SVLs of N females (94.1 cm) and males (111.0 cm) in the final 3 decades were significantly larger than their SVLs in the first decade. The body condition index (BCI) increased over time, and the intrinsic groups differed significantly in mean BCI: N females (−0.0764), G females (0.0146), and males (0.0899). Among recaptured snakes, wide fluctuations of body mass were not uncommon as most snakes experienced annual losses as well as gains. Geographic variation in body size of C. horridus is illustrated by comparing our New York population with a northern population (Massachusetts) and a southern population (Virginia). Across the species' range, we suggest that body size could be associated primarily with prey size. Because many populations of C. horridus are slow growing and long lived, correlated effects of exploitation on body size may negatively affect the snakes' reproductive biology and longevity.ABSTRACT
Linear regressions of body mass vs. snout–vent length for Timber Rattlesnakes (Crotalus horridus) in northeastern New York over all years (1979–2018). Symbols and regression equations as follows: green circles = nongravid (N) females (Y = −896.67 + 16.49X; r2 = 0.969, n = 375); orange circles = gravid (G) females (Y = −981.08 + 18.80X; r2 = 0.978, n = 226); solid triangles = males (M; Y = 1,136.0 + 20.99X; r2 = 0.987, n = 269). All regressions are highly significant (see text).
Time-series scatter plots of body mass recorded over 40 yr in adult Timber Rattlesnakes (Crotalus horridus) in northeastern New York, with best-fitting linear regressions: nongravid females, Y = 594.36 + 3.69X (r2 = 0.708, F = 1,469.5, P < 0.01, total df = 606); gravid females, Y = 792.55 + 2.72X (r2 = 0.801, F = 3,182.8, P < 0.01, total df = 791); males, Y = 1,144.64 + 1.99X (r2 = 0.786, F = 2,052.4, P < 0.01, total df = 560).
Body condition index = log-transformed linear regression residuals over all years in Timber Rattlesnakes (Crotalus horridus) in northeastern New York. Symbols and regression equations: green circles = nongravid females, Y = −0.08983 + 0.00119X (n = 375); orange circles = gravid females, Y = 0.01053 + 0.0004129X (n = 226); solid triangles = males, Y = 0.08138 + 0.0005425X (n = 269).
Sequential body mass records of selected individual Timber Rattlesnakes (Crotalus horridus) in northeastern New York: nongravid females (range of recaptures 3–11 yr); gravid females (range of recaptures 17–26 yr); males (range of recaptures 4–18 yr). Sequential year numbers from 2 (1980) to 38 (2017) as appropriate for capture dates.
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