| Abstract: | The ecology and life history of the Concho water snake was studied in the Colorado Valley region of central Texas during 1988- 1992. These snakes were almost entirely piscivorous, consuming 19 fish species from nine families. The cricket frog, Acris crepitans, represented the only non-piscine prey. Prey size and diversity were correlated with snake body size. Mating activity occurred primarily in late April and early May although fall mating was occasionally observed. Parturition dates ranged from 29 July to 22 September with most births occurring in August. Minimum snout-vent length (SVL) sizes at sexual maturity were 380 mm and 460 mm for males and females, respectively. Approximately 85% of adult females were gravid each year with the proportion of reproductive females in each size class increasing as a function of SVL. Litter size averaged 11.1 embryos (range 4-29) and showed little annual variability. Litter size and mass were positively correlated with female SVL. Litter size had no effect on offspring size when female size was held constant. Concho water snakes were chiefly diurnal with limited crepuscular activity in summer. The seasonal activity pattern was bimodal with activity peaks occurring in May and August. Seasonal activity levels were not correlated with environmental temperatures. Growth patterns usually were described more accurately by the von Bertalanffy growth model than the logistic-by-length or logistic-by-weight models. Females in all populations grew faster and reached significantly larger body sizes than males. The preferred body temperature range of telemetrically monitored adults was 26-32 C with females maintaining significantly higher temperatures than males. Mean movement distances and rates of movement were greater for males than females although mean activity range sizes were similar for each sex. Gravid females became increasingly sedentary and habitat selective as gestation progressed. Juveniles used flat shoreline rocks as refugia with rock size being positively correlated with snake SVL. Mean rock sizes used by neonates increased abruptly from August-October, apparently in response to decreasing temperatures. Snakes were observed to hibernate singly or in small groups within 6 m of water. |
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