Life histories of a species often vary geographically, and comparative studies of populations in different habitats are useful for understanding how environmental variation influences life history. Such studies are currently lacking for most snake species despite their growing importance as model organisms for life history studies. We present life history data for a population of Western Cottonmouths (Agkistrodon piscivorus leucostoma) inhabiting a “riffle–pool” creek system (Rocky Grove) located in the Ozark Mountains in northwest Arkansas and compare our results with those available for other populations. One hundred forty-two individual snakes were captured 283 times from August 1996 through September 2003. Mean snout–vent length (SVL) of adult Rocky Grove A. piscivorus (males 60.8 ± 2.68 cm, n = 47, females 54.9 ± 1.74 cm, n = 47) was among the smallest reported for any population of A. piscivorus. Rocky Grove A. piscivorus also exhibited a low degree of sexual size dimorphism (SSD) compared to other localities, and mean female SVL was 90.3% that of males. Growth rates were the slowest reported for any temperate zone pitviper (males 0.151 ± 0.053 cm/month, n = 46, females 0.178 ± 0.06 cm/month, n = 66). Limited data also indicate low reproductive output for this population in terms of frequency of reproduction and litter size. Female reproduction averaged less than biennial as evidenced by consistently low proportion of pregnant to non-pregnant females (18.4%) and reproductive histories of individual female snakes. Litter size averaged 4.1 ± 0.63 (n = 10). Mating at Rocky Grove occurs in late summer but may also occur in spring. Agkistrodon piscivorus at this study site may be limited in energy acquisition rates relative to the conspecifics in other parts of the range.
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Vol. 2008 • No. 1