Ecology of a Specialized Predator: Regina grahami in Missouri

I studied the ecology of a discrete population of Graham's crayfish snake (Regina grahami) in northwestern Missouri continuously from 1979-1983. As is true of other natricines, females were sig- nificantly longer and heavier than males. Snakes were active from April through early November, with peaks of activity in early spring and late autumn. Regina in this population were mainly diurnal; nocturnal activity was confined primarily to summer months. In comparison with R. grahami from Missouri, snakes in Louisiana began and ended their activity season much earlier and had a unimodal activity pattern. Females in Missouri produced a single brood each year, with a mean brood size of 11.6 (range = 5-16). Larger females produced larger broods. The sex ratio of offspring was skewed in favor of females, and there was evidence of sexual size dimorphism among neonates, with males larger than females in body length but not body mass. All prey items were molting crawfish; feeding frequency was highest among juveniles. Except for sexual dimorphism in offspring size and a biased sex ratio at birth, few major ecological differences were found between R. grahami and other natricine snakes. The crayfish snakes (genus Regina) are an eco- logically specialized group of four species found in the eastern and central United States. Al- though their systematic relationships with oth- er natricine snakes have produced a consider- able debate (cf. Rossman, 1963, 1985; Price, 1983; Lawson, 1987), all adult Regina are highly spe- cialized predators on crawfish (Ernst and Bar- bour, 1989). Although several detailed field