Abstract
We investigated a convenient method for estimating the absolute density of breeding populations of a threatened subtropical passerine, Apalopteron familiare, which is endemic to the Ogasawara (Bonin) Islands. In order to estimate the number of breeding males or pairs, the method takes advantage of the brief dawn chorus period of the species. The number of vocalising males detected, using the method, was very stable during each census period. The detectability of resident males was nearly 90% of the total number of resident males known to be occupying the study area, based on territory mapping of marked birds. Only about 10% of resident, paired males did not sing, thus the method registered almost all males singing in the study site. As few unpaired, singing males were present, the number of males estimated by the method was approximately the same as that of paired males.
