IUCN threat status:

Critically Endangered (CR)

Distribution

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Range Description

Acrocephalus familiaris is endemic to the steep, rocky island of Nihoa in the north-western Hawaiian Islands, U.S.A. It previously occurred on Laysan also, where the nominate race was estimated to number 1,500 birds in 1915, but became extinct between 1916 and 1923. On Nihoa, existing monitoring methods, and data recorded intermittently since the late 1960s, do not yield precise population estimates or trends for this species (Morin et al. 1997, H. Freifeld in litt. 2010). However, the existing data do suggest that Millerbird numbers on Nihoa have experienced pronounced fluctuations and have likely ranged between fewer than 50 and more than 800 individuals (H. Freifeld in litt. 2010), with the most recent estimates of 507 295 individuals in September 2010 and 775 298 individuals in September 2011 (Kohley et al. 2010 VanderWerf et al. 2011). These fluctuations have had a significant impact on the genetic diversity of the remaining population, with the effective number of breeders being estimated as between 5 and 13 individuals (using samples collected in 2007 and 2009 [Addison et al. 2011]). The vegetated area of Nihoa is just 0.43 km2 (68% of the island), and Millerbirds are distributed patchily within this area (H. Freifeld in litt. 2010). A first translocation was undertaken in September 2011 when 24 Millerbirds were moved from Nihoa to Laysan, a distance of 1,037 km (Farmer et al. 2011a). Upon arrival at Laysan the 24 birds were released and each was resighted at least once during the initial three-week period. During the first breeding season on Laysan, nesting birds on Laysan produced at least five fledglings (Kohley and Rutt 2012, J. Vetter, unpublished data).

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Source: IUCN

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