Species

Justification
This poorly known island warbler qualifies as Vulnerable because its very small range leaves it susceptible to chance events, such as cyclones and the introduction of alien predators.

Taxonomic source(s)
Sibley, C. G.; Monroe, B. L. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, USA.

Identification
15 cm. Medium-sized, drab warbler with thin, straight bill. Greyish-olive above, off-white below with white eyebrow. Similar spp. No other passerines on the island. Voice Unreported, but presumably has the chuck call note shared by most Pacific island reed-warblers.

Distribution and population
Acrocephalus rehsei is endemic to the tiny island of Nauru, in the western Pacific Ocean. In 1993, it was found to be widely distributed throughout the island and relatively common (B. Fletcher in litt. 1995) and in 2006 the population was estimated at 5,000 individuals and it was still considered common (Buden 2008). There is little information on trends.

Population justification
Buden (2008) estimated the population at 5,000 individuals. This estimate is equivalent to 3,333 mature individuals, rounded here to 3,000 mature individuals.

Trend justification
The species can utilise any scrubby vegetation, therefore, in the absence of introduced predators its population remains stable.

Ecology
It occurs at highest densities in remnant forest on the steep sides of the island escarpment, but is also frequently found in gardens and rural areas in coastal areas and in previously mined, but now regenerating areas of scrub, thickets, and remnant forest patches on the central plateau (B. Fletcher in litt. 1995, Buden 2008). In coastal areas, it forages for insects in the crowns of coconut trees (B. Fletcher in litt. 1995) and has been observed apparently gleaning insects from foliage in shrubs and among the branches of small trees as well as sallying from a low perch and apparently foraging on the ground in open, sparsely vegetated areas (Buden 2008). Stephen (1936) reported this species nesting on the ground; however Buden (2008) observed disused nests 2-8 m high in shrubs and trees.


Threats
Nearly 80 years of phosphate mining has caused devastating environmental damage to the island (Anderson 1992), but extraction is now carried out on only a small scale and the species has proved able to colonise regenerating areas (B. Fletcher in litt. 1995). There is no information on other possible threats, such as predation by introduced rats Rattus spp. which have caused severe declines in other small-island Acrocephalus species. Buden (2008) reports an apparent incident of a nest that may have been predated by rats, but this is purely speculative. The species might be at risk from cyclones, given its small range, however its broad habitat preferences suggest a high resistance to such events.


Conservation actions underway
None is known.

Conservation actions proposed
Re-survey the population regularly to monitor trends. Provide training to local people so that an on-going monitoring programme can be established (SPREP 2000). Increase the profile of this endemic bird to raise conservation awareness on Nauru (SPREP 2000).

Related state of the world's birds case studies

• Many threatened birds are restricted to small islands

References
Anderson, I. 1992. Can Nauru clean up after the colonists? New Scientist 1830: 18-19.

SPREP. 2000. Proceedings of the Melanesian Avifauna Conservation Workshop, Nadi, Fiji, 5-10 March, 2000.

Buden, D.W. 2008. The birds of Nauru. Notornis 55(1): 8-19.

Stephen, E. 1936. Notes on Nauru. Oceania 7: 34-63.

Further web sources of information
View photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Derhé, M., Mahood, S., O'Brien, A., Shutes, S., Stattersfield, A.

Contributors
Buden, D., Fletcher, B.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2013) Species factsheet: Acrocephalus rehsei. Downloaded from http://www.birdlife.org on 26/05/2013. Recommended citation for factsheets for more than one species: BirdLife International (2013) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 26/05/2013.

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.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.