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Rediscovery of Large-billed Reed Warbler Acrocephalus orinus 139 years after the capture of the only previously known specimen
Compelling evidence has been released of the continuing existence of the Large-billed Reed Warbler Acrocephalus orinus, previously known only from the unique type specimen collected in NW India 139 years ago.

Large-billed Reed Warbler
Acrocephalus orinus
(Photo by Philip D. Round)

This small, unstreaked Acrocephalus warbler (pictured left) was caught during routine monitoring and ringing of migratory birds in conjunction with the Wildlife Research Division of the Department of National Parks and the royally initiated Laem Pak Bia Environmental Research and Development Project, Phetchaburi Province, SW Thailand, approximately 3,100 km from the type locality, on 27 March 2006.

The type specimen of A. orinus was recently re-examined (Bensch and Pearson 2002), confirming its status as a bona-fide species. Morphological and genetic analyses of the Laem Pak Bia bird confirmed its identity as A. orinus, and revealed that there was sufficient genetic variation to indicate the continued existence of a viable population.

Whilst this species is an addition to the Thai list, where the population might breed or winter is still unknown. This, just the second record ever, does not throw much light on where A. orinus might normally be found. The fact that both records occurred in the northern hemisphere's winter period and that the closest relative, Blyth's Reed Warbler A. dumetorum, winters in southern Asia, it is thought that A. Orinus probably breeds somewhere in the Palaearctic, wintering in southern Asia, most likely to the west of Thailand, possibly in Myanmar or the Indian subcontinent. It is quite possible that it could winter alongside Blunt-winged Warbler A. concinens, or A. dumetorum, but has remained undetected due to its close similarity to these species in the field.

The location of capture at Laem Pak Bia is a small area of grass filter beds in a royally initiated wastewater treatment project in Phetchaburi Province, Thailand. It is located in an area of otherwise brackish water, in which the dominant land-use is salt pans, and separated from the coast by a 500 m-wide belt of regenerating mangroves. Most of the wastewater treatment project consists of five large water treatment ponds which lack fringing vegetation.

From 2000-2006 approximately 200 individuals each of Black-browed and Oriental Reed Warbler have been caught.and ringed, with A. orinus being the only other Acrocephalus warbler having been encountered.

Location of Capture

Large-billed Reed Warbler Acrocephalus orinus
(Photo by Philip D. Round)

100 kilometres further south, extensive ringing of Acrocephalus warblers has been carried out in the Phragmites reedswamp at Khao Sam Roi Yot, yet A. orinus has never been recorded there.

These facts perhaps indicate that the core habitat of A. orinus is something other than Phragmites, and certainly suggest that it is an extreme vagrant specifically to this region and probably to Thailand in general.

Since this amazing rediscovery, another specimen has been confirmed, using DNA analysis, from a collection in Tring, UK. Read more Birdlife International.



This article was compiled using information from Round et al. (2007). Lost and found: the enigmatic large-billed reed warbler Acrocephalus orinus rediscovered after 139 years, Journal of Avian Biology 38, pp 133-138 (March 2007) kindly sent to me by Philip D. Round.

More photographs and details of the rediscovery of Large-billed Reed warbler as well as comparison with similar species on the BCST website.

Read an interview with Philip D. Round about Large-billed Reed Warbler on Ornithomedia.

A probable sighting of Large-billed Reed Warbler in the wild has been made near Kolkata, India. April 2007.

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