The Nightingale Reed-warbler (Acrocephalus luscinia) is an endangered songbird of the Mariana Islands. The Chamorro name for the bird is ga`ga` karisu (bird of the reeds).
The species is approximately 17 cm (7 inches) long, and is greyish olive-brown above with a pale-yellow underside. It inhabits wetlands, thickets and the margins of forests. the female is slightly smaller than the male, both sexes have a long bill compared to other reed warbler species.
The nightingale reed-warbler can be found on the Northern Mariana Islands of Saipan and Alamagan. Until the late 1960s the bird was also on Guam. An alien species, the brown tree snake is primarily blamed for its demise on the island. It is estimated that roughly 6200 birds remain, with 4200 on Saipan and 2000 on Alamagan.
Historically there were three subspecies of Acrocephalus luscinia that are either extinct or presumed extinct:
- Aguijan Nightingale Reed Warbler, Acrocephalus luscinia nijoi: a handful of the subspecies were known to exist in the mid-1980s on the uninhabited island of Aguijan.
- Astrolabe Nightingale Reed Warbler, Acrocephalus luscinia astrolabii : known from only two specimens, believed to have gone extinct in the mid-19th century.
- Pagan Nightingale Reed Warbler, Acrocephalus luscinia yamashinae: considered to be extinct since the 1970s on Pagan Island.