Presumed hybrid Blyth's Reed Acrocephalus dumetorum x Marsh Warbler A. palustris trapped at Ngulia, Kenya,in December 2009

摘要

On 17 December 2009 an unusual-looking Acrocephalus was trapped at Ngulia Lodge in Tsavo West National Park, south-east Kenya. It was one of several hundred Palearctic passerines mist-netted at dawn, mainly Marsh Warblers A. palustris, grounded afterbeing attracted to lights during the previous misty night. Being freshly moulted it immediately stood out from the unmoulted Marsh Warblers with which it was directly compared. Its uniform, rather dark olive-brown upperparts also appeared to eliminate Eurasian Reed Warbler A. scirpaceus which can occur (race fuscus) fully moulted at Ngulia in December. A quick check of the wing formula eliminated both species, for p2 (numbered ascendently) was short, falling between pp5-6, whilst pp3^4 had an emarginated outer web. A wing length of 68 mm eliminated any race of the much smaller African Reed Warbler A. baeticatus but also seemed long for Blyth's Reed Warbler A. dumetorum. The bird was, however, tentatively identified by DP, IK & BA as a Blyth's Reed Warbler, a view supported by its leg and iris colours, which differed from those typical of either Marsh or Eurasian Reed Warblers. The chestnut-brown eye indicated that it was an adult. Photographs, measurements and a detailed description were taken, and asmall blood sample was collected for DNA analysis. The bird was ringed and released at the site of capture.