Brown Tree Snake

The brown tree snake is a nocturnal, arboreal species that uses both visual and chemical cues when hunting, whether in the rainforest canopy or on the ground. It is a member of the subfamily Colubrinae, genus Boiga, which is a group of roughly twenty-five species that are referred to as "cat-eyed" snakes for their vertical pupils. The brown tree snake is generally 1–2 metres (3–7 ft) in length in its native range. The snake is long and slender, which facilitates its climbing ability and allows it to pass through tiny spaces in buildings, logs, and other shaded locations, where it seeks refuge during daylight. Variations in coloration occur in the snake's native range, from lightly patterned brown to yellowish/green or even beige, with red, saddle-shaped blotches. They are rear-fanged, have a large head in relation to their body, and can survive for extended periods of time without food. The median age of maturity for these snakes is estimated to be 3.1 years in males and 3.7 years in females. Owing to the availability of prey and the lack of predators in introduced habitats such as Guam, they have been known to grow to larger sizes than their typical 1 to 2 m (3.3 to 6.6 ft) in length. The longest recorded length of this species is one found on Guam measuring 3 m (9.8 ft).

The brown tree snake is native to coastal Australia, Papua New Guinea, and many islands in northwestern Melanesia. The species occurs on variably sized islands, extending from Sulawesi in eastern Indonesia through Papua New Guinea and the Solomon Islands and into the wettest coastal areas of Northern Australia. The snakes on Guam represent the only documented reproductive population outside the native range. Since January 2016, however, four snakes have been sighted on the island of Saipan in the Northern Mariana Islands. A separate species, Boiga flavescens, was described from Sulawesi in the nineteenth century. Subsequent authors identified both B. flavescens and B. irregularis on the island, and flavescens was synonymised with irregularis in 1985 by In den Bosch. Weinell et al. found significant DNA differences between the Sulawesi and Sundaland populations, proposing in 2021 that all members west of Weber's Line be designated B. flavescens. The brown tree snake is not restricted to forested habitats; it also occurs in grasslands and sparsely forested areas. In Papua New Guinea, it occupies a wide variety of habitats at elevations up to 1,200 m. It is most commonly found in trees, caves, and near limestone cliffs, but frequently comes down to the ground to forage at night. …

In its native range, the brown tree snake preys upon birds, lizards, bats, and mice and other small rodents. Those of a smaller size focus on smaller prey such as frogs and lizards, while the larger individuals prey on larger vertebrates such as mammals and birds. The larger snakes are often seen shifting their diet towards endotherms rather than consuming ectotherms due to relative prey size. On Guam, this shift is prevalent because the island's prey is mostly larger ectotherms, such as lizards, which are the primary prey for smaller snakes and birds. The snake preys on a large variety of invertebrates, including their eggs, their young, and the adults of many of the preyed upon species. A study was done on the Guam population where 683 snakes were necropsied, and their stomach contents were examined. The majority of stomach content consisted of reptiles and reptile eggs, followed by birds and bird eggs, and then lastly mammals. The snake also preys on shrews on Guam, and threatens native bird and lizard species.