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Abstract
Population parameters, habitat, diet, reproductive traits, and other natural history characteristics of the brown water snake, Nerodia taxispilota, from the Savannah River Site, South Carolina, USA, were determined or estimated using mark-recapture data collected over an 8-yr period (1991-1998). Population size estimates for a 10-km section of the Savannah River ranged from 2782 - 3956 (approximately 0.14 - 0.20 snakes/m of shoreline). Growth was similar in juveniles of both sexes, but adult females grew significantly faster than adult males. Life history traits for this population include: 1) relatively high adult survivorship, 2) estimated ages at maturity of approximately 5-6 years for females and 3 years for males, 3) relatively long-lived (6+yr) individuals, 4) high fecundity (mean litter size =18.2), and 5) annual reproduction by females larger than 115 cm SVL. Litter size was positively correlated with female length and mass. No apparent trade-off exists between litter size and offspring size. Brown water snakes were not randomly distributed and were significantly associated with the steep-banked outer bends of the river and availability of potential perch sites. River sections with the highest number of captures were clustered within 200 m of backwater areas. Most (70%) of 164 recaptured N. taxispilota were <250 m from their previous capture site; however, three moved >1 km. Only large (>80 cm snout-vent length) individuals (n = 8) crossed the river (approximately 100 m). I collected foraging and dietary information from 1565 individual captures by using a nonlethal, albeit labor intensive, technique. Of all captures, 257 (16%) had food in their gut, and of the identifiable food items (n=168) all were fish and 63% were catfishes (Ictaluridae). A significant shift to an almost exclusively catfish diet occurred in snakes greater than about 60 cm SVL. Of 814 females captured, 18% had eaten, compared to 15% of 748 males. Feeding frequency (percent captured with food) ranged from 15.8%-20.3% between four general study sites and varied monthly, with peak frequencies in May, July, and October.