Endangered Species in the Pacific Islands

Nightingale Reed-warbler / Acrocephalus luscinia  / ga‘ga‘ karisu

The endangered nightingale reed-warbler, known in Chamorro (one of the native languages of the Mariana Islands) as ga‘ga‘ karisu (bird of the reeds), measures about 7 inches (17 centimeters) in length. It is yellowish below and darker brown/yellow above. Compared to other reed-warblers found from Europe through Australasia, the reed-warbler found in the Marianas is a large and very long-billed species. Males are larger than females in size but do not significantly differ from females in bill length.

Nightingale reed-warbler - Photo credit Scott Vogt

Habitat & Behavior:
Reed-warblers are widespread from Europe through Australasia, with as many as 10 species presently represented in the tropical Pacific. The relatively large, long-billed nightingale reed-warbler of the Mariana Islands is among the most distinctive.

Most birds found on the island of Saipan occur in thicket-meadow mosaics, tangan tangan (Leucaena leucocephala), reed marshes, and wetlands. The population of nightingale reed-warblers on Alamagan inhabits areas with open brushy overstory and understory, and wooded edges adjacent to open grassland.

Male nightingale reed-warblers show high site fidelity, defend their territories by singing, and tend to remain in the same territory though the boundaries may change. Females are more likely to change territories than males. The nightingale reed-warbler song is varied and complex, loud and melodious, and they often sing at night. They have been observed to feed on insects, spiders, snails, and lizards. Prehistorical evidence indicates the species once occurred on Tinian.

Past & Present:
Three subspecies of nightingale reed-warbler are currently recognized in the Mariana Islands: Acrocephalus luscinia luscinia (Guam, Saipan, Alamagan), Acrocephalus luscinia nijoi (Aguiguan), and Acrocephalus luscinia yamashinae (Pagan). The validity of these subspecies warrants further study, however.

Of the three recognized subspecies, Acrocephalus luscinia luscinia, originally found on Guam, Saipan, and Alamagan, has been extirpated on Guam since the late 1960s. Acrocephalus luscinia nijoi of the presently uninhabited island of Aguiguan was first reported in 1940 by a Japanese collector, and surveys conducted by the Commonwealth in 1983 and 1985 yielded a maximum count of six individuals. Nightengale reed-warblers have not been observed there since 1995 and may be extirpated. Acrocephalus luscinia yamashinae of uninhabited Pagan is believed to have survived in small numbers until at least the 1960s. The population is now thought to be extirpated. The total number of nightingale reed-warblers is approximately 2,770-3,599 pairs distributed over three islands: Aguiguan (1-3), Saipan (2,596), and Alamagan (173-1,000).

Past and present threats to populations include loss and degradation of habitat (including wetland destruction), predation by introduced predators such as the brown treesnake, rat, and monitor lizard, feral ungulates, and vulcanism.

Conservation Efforts:
The nightingale reed-warbler is protected by the Endangered Species Act of 1973 and is also listed as an endangered species by the Commonwealth of the Northern Mariana Islands and the Territory of Guam

The recovery strategy identified by the U.S. Fish and Wildlife Service's Recovery Plan for the nightingale reed-warbler is to protect the existing populations of the Nightingale Reed-warbler and the habitat on which they depend. Most importantly, this species will need protection from the threat of introduction of the brown treesnake. Habitat protection will involve establishment of sanctuaries and elimination of feral ungulates and possibly predator control, where appropriate. The recovery plan also recommends the continuance of research and translocating reed-warblers from Saipan and/or Alamagan onto at least three additional islands.