High Nest Predation by Brown Tree Snakes on Guam

Abstract

A great deal of attention has recently been focused on the drastic decline of the native avifauna of Guam since the 1960s (Ensbrina 1983: Jenkins 1983: Enebrine and Ramsey 1984,Savidge 1984, 1986, 1987).Pipulations of once common native forest birds have declined and are now thought to be locally extinct or restricted to the northernmost part of the island (Jenkins 1983; Engbring and Ramsey 1984; U.S. Fish and Wildlife Service, in press).Savidge (1986, 1987) investigated the role of disease and predation in the decline and concluded that the introduced brown tree snake (Boiga irregularis) was responsible for the extinction or decline of 10 species of native forest birds on Guam.My report provides direct evidence of the significant impact that snake predation is having on the nesting success and population dynamics ofthe Philippine Turtle-Dove (Streptopelia bitorquata), one of the few wild birds on Guam that remains sufficiently abundant for such a study.The Philippine Turtle-Dove was probably introduced to the Mariana Islands by the Spanish in the late 1700s (Baker 195 1).The species became one of the most abundant birds on Guam and was made a legal game bird (Baker 1947, 1951: Conrv 1987).More recently, however, numbers have declined in a pattern similar to that of the native forest birds, though not as severely, and the hunting season for the species has been closed (Engbring and Ramsey 1984, Conry 1987).The turtle-dove is presently uncommon to rare throughout southern Guam, common in localized areas of central and northern Guam, and abundant on Cocos Island, a small snake-free islet 2 km off southern Guam (Conry 1987).The turtle-dove also occurs on the neighboring southern Mariana Islands of Rota, Aguijan, Tinian, and Saipan (Pratt et al. 1987) where its numbers appear stable (T.K. Pratt, pers.comm.) and the brown tree snake does not occur.STUDY AREA AND METHODS Nesting success of the Philippine Turtle-Dove was studied in forest and urban habitats on Andersen Air 1