Justification This species has been uplisted to Critically Endangered because the very rapid rate of decline in its very small global population observed over the past three generations is expected to increase owing to habitat loss and degradation combined with the impact of brown tree snake Boiga irregularis on Saipan; this snake has already led to the reed-warbler's extirpation from Guam.

Family/Sub-family Sylviidae

Species name author (Quoy & Gaimard, 1830)

Taxonomic source(s) Sibley and Monroe (1990, 1993)

Synonyms Acrocephalus luscinia BirdLife International (2000), Acrocephalus luscinia Collar et al. (1994), Acrocephalus luscinia Sibley and Monroe (1990, 1993)

Taxonomic note Gender agreement of species name follows David and Gosselin (2002a).

Identification 18 cm. Large, lanky, scruffy-looking warbler with long bill and often dishevelled feathers. Dingy olive-yellow above, with dull yellow eyebrow and underparts. Voice Call a loud distinctive chuck or tchack. Song long, loud, varied, and complex. Hints Skulks in dense thickets, more often heard than seen. Sometimes sings at night.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

2,000 - 2,499

decreasing

140 km²

Yes

Range & population Acrocephalus luscinius is historically known from Guam (to USA), Saipan, Alamagan, Aguijan and Pagan in the Northern Mariana Islands (to USA). It was extirpated from Guam in the late 1960s, and from Pagan before 1981. A tiny population perhaps survives on uninhabited Aguijan (1-6 birds) and on Alamagan (c.346), but the majority of the population occurs on Saipan. Abundance (density times the area of Saipan, 115.39 km²) with 95% Confidence Intervals declined from 6,658 birds (5,331-8,054) in 1982 down to 4,639 (3,669-5,689) birds in 1997, and has continued to decline to 2,596 birds (1,985-3,254) in the 2007 survey⁹. This represents a 61% decline in the species since 1982. Over three generations this equates to an overall population decline of 44%, but this rate of decline has been increasing such that the rate recorded between 1997 and 2007 corresponds to a three generation decline of 60%. The rapid human expansion on Saipan in the 1990s has slowed but the U.S. military is expanding its presence and operations which will likely lead to further habitat conversion and degradation. Furthermore, there is evidence that the Brown Tree Snake Boiga irregularis has become established on Saipan. This is cause for concern given the catastrophic declines it caused on Guam's birds. The combination of these two drivers is expected to lead to projected declines above 80% over 3 generations in the future.

Ecology: On Saipan, it occurs in thicket-meadow mosaics, forest edge, reed-marshes and forest openings¹. A recent study on Saipan found nests in upland introduced tangantangan forest, a native mangrove wetland and a native reed wetland⁵. On Alamagan, it inhabits open forest with brushy understorey and wooded edges adjacent to open grassland. On Aguijan, it inhabits formerly disturbed areas vegetated by groves of trees and thickets. On Guam and Pagan, it was almost exclusively found in freshwater wetland and wetland edge vegetation^2,3,4.

Threats On Guam, several factors in combination are likely to have caused the species's extirpation, including wetland destruction, predation by the introduced brown tree snake Boiga irregularis, pesticide-use and major fires. On Saipan, available habitat has been reduced for agriculture, home-building and tourist-related facilities. The brown tree snake is now understood to be established on Saipan and unless it can be controlled the population is likely to be extirpated rapidly once snake numbers have reached the point where they impact bird populations. On Aguijan, feral goats severely degrade habitats⁶. Introduced predators, including monitor lizard Varanus indicus, feral cats and rats Rattus spp., may be a large factor in the reported high proportion of nest failures⁴.

Conservation measures underway A recovery plan exists but there has been little or no active management for the species to date. However, provisions to protect habitat and mitigate loss have generally been included in major land development projects. In 1989, a goat removal programme was begun on Aguijan but, by 1995, goat populations had begun to rebound with reduced hunting pressure. Trap lines for snakes are maintained at ports, night searches are conducted and a sniffer dog programme has recently been established. Publicity campaigns aim to raise the general awareness of island residents, including port workers, about the dangers of snake colonisation⁴. Repeat surveys have been conducted on Saipan in 1982, 1997 and 2007.

Conservation measures proposed Monitor the populations on all three islands⁴. Protect Aguijan, and especially Alamagan from snake colonisation⁴. Control feral ungulates and predators including B. irregularis⁴. Identify and protect essential habitat⁴. Conduct basic research, e.g. on population dynamics and validity of subspecies, to assist in appropriate recovery efforts⁴. Establish additional populations on other islands⁴. Clarify the status of B. irregularis on Saipan and mitigate the potential effects should its number increase.

References 1. Craig (1996). 2. Engbring et al. (1982). 3. Reichel et al. (1992). 4. USFWS (1998). 5. Mosher and Fancy (2002). 6. A. Saunders in litt. (2003). 7. H. Freifeld in litt. (2007). 8. Camp (2008). 9. Camp et al. (in review).

Further web sources of information

U.S. Fish and Wildlife Service - Recovery Plan

Text account compilers Phil Benstead (BirdLife International), Jeremy Bird (BirdLife International), Simon Mahood (BirdLife International), Andrew O'Brien (BirdLife International), Alison Stattersfield (BirdLife International)

Contributors Rick Camp (US Geological Survey), Guy Dutson (Birds Australia), Holly Freifeld (US Fish & Wildlife Service), Alan Saunders (Department of Conservation)

IUCN Red List evaluators Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International)

Recommended citation BirdLife International (2009) Species factsheet: Acrocephalus luscinius. Downloaded from http://www.birdlife.org on 10/2/2010

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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