Abstract
The Thick-billed Warbler Acrocephalus aedon normally breeds from southwestern Siberia across the continent to the Amur River region on the Pacific seaboard, and winters from India to Indochina. An eastern and western subspecies are recognized. Previously only one record had been obtained in Japan, in Nagano Prefecture in May of 1927. On 5 February 1997, an individual of this species was sighted on riverside farmland near the mouth of the Fuji River, in Shizuoka Prefecture. This individual was netted on 13 February, and judged to be a juvenile in first winter plumage. The bird was banded and released, and observed to remain in the vicinity until 16 April. The area in which the warbler foraged is warmed by waste water constantly discharged from a nearby factory. The bird was observed feeding on bloodworms (Chironomus sp.).
