U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

January 2001


The brown tree snake (Boiga irregularis) is a nocturnal, arboreal, rear-fanged, mildly venomous, colubrid snake which can reach lengths of up to 2.3 m and weigh as much as 2 kg(1). Originally, the species' range included the northern and eastern coasts of Australia, Papua New Guinea and nearby islands (2). It is believed that sometime in the 19501s, that snakes were inadvertently transported from New Guinea to Guam, where they proliferated (3). By the mid-1960’s, marked decreases in Guam's bird life were observed. By the mid-1980’s, snake densities were estimated at 50 to 100/hectare (13,000 to 26,000/sq mile), higher densities than those recorded for any other snake (3,4).

Brown tree snakes are dietary generalists, being observed to eat chicken bones, cooked spare ribs, lizards, birds, rodents, domestic fowl hatchlings, puppies, piglets, rabbits (in hutches), and pet birds (in cages inside homes) (1,5). Human irritants have also been attacked, resulting in very serious bites (6,7). Snake predation has resulted in the extirpation or severe reduction in the populations of virtually all Guam's avifauna and has essentially resulted in the extinction of four endemic species/subspecies: 1) Bridled white-eye (Zosterops conspicillatus conspicillatus), 2) Guam flycatcher (Myiagra freycineti), 3) Micronesian kingfisher (Halcyon cinnamomina cinnamomina), and 4) Rufous fantail (Rhipidura rufifrons uraniae) (8,9). The Mariana crow (Corvus kubaryi) has also been severely reduced, with 8 birds remaining on Guam, and an additional 300 to 600 remaining on the nearby island of Rota (10). The crow is listed as an endangered species and, as a scavenger that might consume lethally-dosed snake carcasses resulting from chemical toxicant control operations, plays a significant role in secondary hazard assessments of the use of such toxicants.