Nightingale reed-warbler (Acrocephalus luscinius)

Synonyms: Acrocephalus luscinia
GenusAcrocephalus (1)
SizeLength: 18 cm (2)
Average male weight: 35.9 g (3)
Average female weight: 32 g (3)

Classified as Critically Endangered (CR) on the IUCN Red List (1).

The nightingale reed-warbler is known locally as ga’ga’ karisu, meaning ‘bird of the reeds’, a somewhat misleading title given its occupancy of a number of diverse habitats (4). It is a relatively large reed-warbler with an especially long bill, contributing to its rather lengthy, slender appearance (4) (5). Both sexes are similar in appearance, with the upperparts, tail and wings being olive-yellow, while the underparts are dull golden yellow (5) (6). A clearly defined black stripe cuts through the eye and a crown of scruffy feathers sits atop the head (2).

The song of the nightingale reed-warbler is both distinctive and complex, comprising a number of loud whistles, warbles, and trills (2). This long song can be heard at night and often at dawn when males sing in a chorus, and is less frequently heard during the day (2) (5).

Historically, the range of the nightingale reed-warbler stretched across six of the Northern Mariana Islands in the western Pacific Ocean, from Pagan in the north to Guam in the south (4) (7). Currently, however, it is only found on three of these islands: Saipan, Alamagan and Aguijan (2).

The nightingale reed-warbler is predominantly found in mangroves, thickets, reed marshes and mosaics of elephant grass (Pennisetum purpureum) and tangan-tangan (Ricinus communis) (2) (3) (4). However, it has also been found in forest edges, forest openings, and areas formerly disturbed by events such as typhoons (6).

Little is known about the diet of the nightingale reed-warbler, although the bulk of it is likely to comprise insects, lizards, spiders and snails (2). Although this bird predominantly forages on the ground, it has been known to also gather invertebrates from leaves and from dead tree stumps (2).

The nightingale reed-warbler breeds between January and March, and between July and September. It forms monogamous pairs, with the female building the nest and the male defending the territory (2) (3) (8). The nest is usually constructed in the branches of the tangan-tangan tree, and is made from vine stems, grass blades, bark strips, and sometimes spider webs (8). The male uses song to defend its territory, perching on a branch or exposed tree top in order to be clearly seen and heard by other males (3).

The story of how the nightingale reed-warbler was extirpated from Guam, Pagan and Tinian is one echoed by many island species across the world. Human impact, through habitat destruction and the use of harmful insecticides (such as DDT), combined with natural factors, such as volcanic activity and widespread fires, are thought to be partially responsible (4) (5) (6) (9). However, the largest impact on the nightingale reed-warbler has been from the introduction of the brown tree snake (Boiga irregularis), believed to be responsible for the warbler’s final extirpation from Guam in 1969 (2) (4).

The other Mariana Islands receive virtually all their supplies from Guam and the brown tree snake is often a stowaway in cargo (10). As a result, a population of brown tree snakes has already been established on Saipan and there is a very high risk it will reach Alamagan and Aguijan (6). The brown tree snake, in combination with habitat loss for home building and tourism and the introduction of cats and rats, has led the Saipan population of nightingale reed-warblers to fall from 6,658 birds in 1982 to only 2,596 birds in 2007 (4) (6) (9). The much smaller Alamagan and Aguijan populations, estimated in 1997 to contain just 346 birds and up to 6 birds respectively, could easily be devastated by the arrival of the brown tree snake (4) (6) (9).

A great deal of conservation work has been, and continues to be, undertaken to ensure the survival of this Critically Endangered bird. Currently, it is protected by the U.S. Endangered Species Act, making it illegal to hunt, kill, or possess a nightingale reed-warbler or its eggs. Furthermore, the wetland habitats where a great number of populations live are protected under the U.S. Clean Water Act and in 1998 a recovery plan for the species was produced by the U.S. Fish and Wildlife Service (4) (11).

The maintenance of traps and the establishment of a sniffer dog team based in ports and airports around the Northern Mariana Islands are measures aimed at preventing the movement of brown tree snakes onto the islands of Alamagan and Aguijan (4). In addition, 2002 saw the creation of a protected area in Saipan, where the nightingale reed-warbler is monitored, while being provided protection from humans and invasive species (4) (11). These conservation measures are aimed at increasing the number of nightingale reed-warblers on Saipan, Alamagan and Aguijan and hopefully, if they are successful, the species may be re-introduced to the islands of Tinian and Pagan in the future (4).

For more information on conserving Critically Endangered birds see:

 To find out more about wildlife conservation in the Mariana Islands see:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. IUCN Red List (May, 2010)
  2. del Hoyo, J., Elliott, A. and Sargatal, J. (2006) Handbook of the Birds of the World. Volume 11: Old World Flycatchers to Old World Warblers. Lynx Edicions, Barcelona.
  3. Craig, R.J. (1992) Territoriality, habitat use and ecological distinctiveness of an endangered Pacific island reed-warbler. Journal of Field Ornithology, 63(4): 436-444.
  4. U.S. Fish and Wildlife Service (1998) Recovery Plan for the Nightingale Reed-Warbler (Acrocephalus luscinia). U.S. Fish and Wildlife Service, Portland, Oregon.
  5. Marshall Cavendish Corporation (2001) Endangered Wildlife and Plants of the World. Volume 12. Marshall Cavendish, New York.
  6. BirdLife International (May, 2010)
  7. Reichel, J.D., Wiles, G.J. and Glass, P.O. (1992) Island extinctions: the case of the endangered nightingale reed-warbler. The Wilson Bulletin, 104(1): 44-54.
  8. Bocheñski, Z. and Kuœnierczyk, P. (2003) Nesting of the Acrocephalus warblers. Acta Zoologica Cracoviensia, 46(2): 97-195
  9. Temple, S.A. (1985) Bird Conservation 2. The University of Wisconsin Press, Wisconsin.
  10. Marzluff, J.M. and Sallabanks, R. (1998) Avian Conservation: Research and Management. Island Press, Washington.
  11. Abbott, T., Pangelinan, A. and DeCruz, T. (2002) Management Plan for Nightingale Reed-Warblers in the Saipan Upland Mitigation Bank. Division of Fish and Wildlife, Department of Land and Natural Resources, Commonwealth of the Northern Mariana Islands, Saipan.