- Acrocephalus luscinius
Identification
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 the size of the bill remains the same in both sexes.
Distribution
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.
Taxonomy
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. Acrocephalus luscinia yamashinae of uninhabited Pagan has been little studied, and 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 6,225-6,230 individuals distributed over three islands: Aguiguan (1-6), Saipan (4,225), and Alamagan (2,000).
Habitat
Most birds found on the island of Saipan occur in thicket-meadow mosaics, forest edges, reed marshes, and wetlands. On Aguiguan, reed-warblers inhabit formerly disturbed areas vegetated by groves of trees and thickets three to seven feet tall, that may be similar to some habitats utilized on Saipan. On both Guam and Pagan, the species is reported to have inhabited freshwater wetland and wetland-edge vegetation almost exclusively. The population of nightingale reed-warblers on Alamagan inhabits areas with open brushy overstory and understory, and wooded edges adjacent to open grassland.
Behaviour
The Nightingale Reed-warbler has a loud call that sounds like Achuck. Their 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.
