Mariana Swiftlet

The Mariana swiftlet, known scientifically as Aerodramus bartschi, is a small bird measuring approximately 11 centimeters in length. It presents a dark grey-brown coloration on its head and upperparts, while its throat and upper breast are a lighter grey-white. The underparts are a darker shade of grey, and the tail is characterized by a shallow fork. Notably, the plumage of this swiftlet lacks any glossy sheen.

Identification Tips

When attempting to identify the Mariana swiftlet, look for its relatively uniform grey-brown upperparts and the contrast with its grey-white throat and upper breast. The absence of gloss on the plumage and the shallow fork in the tail are also key characteristics to distinguish it from similar species.

Habitat

This swiftlet inhabits tropical moist lowland forests, mangrove forests, and grasslands. It is particularly adapted to life in limestone caves where it roosts and nests.

Distribution

The Mariana swiftlet is native to Guam and the Northern Mariana Islands, specifically Saipan and Aguiguan. It has been introduced to Oahu in the Hawaiian Islands, where a small population persists. Historically, it was found on Rota and Tinian but is now locally extinct in these locations.

Behaviour

The Mariana swiftlet is a colonial nester, building shallow nests on the walls and ceilings of dark limestone caves. It lays a single egg per clutch and may breed multiple times a year. These swiftlets are known for their aerial feeding habits, catching small insects in flight. They use echolocation clicks to navigate within their dark nesting caves and communicate with twittering and chirping sounds. At dawn, the swiftlets typically leave the cave to forage, returning at sunset.

Status and Conservation

Classified as Endangered, the Mariana swiftlet has faced population declines due to predation by brown tree snakes and the use of agricultural pesticides. Conservation efforts are focused on population monitoring, limiting cave disturbances, preventing the spread of brown tree snakes to other islands, controlling pests that damage nests, and considering reintroduction to areas where the species has been extirpated.