Justification of Red List Category
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.
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.
The species can utilise any scrubby vegetation, therefore, in the absence of introduced predators its population remains stable.
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.
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.
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.
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.
Text account compilers
Derhé, M., Mahood, S., O'Brien, A., Shutes, S., Stattersfield, A.
Fletcher, B., Buden, D.
BirdLife International (2019) Species factsheet: Acrocephalus rehsei. Downloaded from http://www.birdlife.org on 21/04/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 21/04/2019.