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.

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 of the species.

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.

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.