Food Habits of Boiga irregularis, an Introduced Predator on Guam

Abstract

Introduced brown tree snakes (Boiga irregularis) from a variety of habitats on Guam were examined for prey remains to determine how B. irregularis has maintained its population despite the overexploitation or extinction of its more vulnerable prey, principally birds and small mammals. Stomach and intestinal tract analyses revealed that B. irregularis consumes primarily birds and their eggs, small mammals, lizards, and lizard eggs. The snakes appeared to be somewhat opportunistic in prey choice. No significant differences were found in the overall diets of males and females of the same size classes. Ontogenetic differences in diet were present. Birds and small mammals were consumed by medium to large snakes; the abundance of both of these prey classes has been severely affected by B. irregularis. Small lizards in general are very abundant on Guam and appear to be an important food source for maintaining small to medium-sized snakes. The overlap of lizard and larger vertebrate prey taken by the intermediate- sized snakes allows the snake population to maintain relatively high densities despite the overexploitation of its larger prey. Boiga irregularis, an arboreal, nocturnal snake, is responsible for the extinctions and range reductions of Guam's forest avifauna as well as the decline of several introduced species of birds and small mammals (Sav- idge, 1986, 1987). There are relatively few studies on the diets of tropical arboreal snakes because of their low densities and secretive nature and no detailed accounts