Surveying Wintering Warbler Populations in Jamaica: Point Counts with and without Broadcast Vocalizations

Abstract

Two independent methods were used to quantify abundances and population structure of two paruline wood warblers, the American Redstart (Setophaga ruticilla) and Black-throated Blue Warbler (Dendroica caerulescens), wintering in Jamaica, West Indies. One conventional 10-min point count was followed by 5 min each of redstart, then Blackthroated Blue Warbler vocalizations (a mixture of territorial songs and chip notes recorded during the breeding season) at each of 585 points in 18 habitats. Age and sex composition of the target species were recorded along with observations of other species. Compared with conventional point counts, those supplemented with playback of vocalizations (1) detected 3.0 and 2.3 times more American Redstarts and Black-throated Blue Warblers, respectively, (2) disclosed significantly more individuals of three other migrant species and one year-round resident species belonging to the warbler guild, (3) facilitated identification of age and sex of target species by attracting them closer to the observer, and (4) confirmed that wintering individuals of both species of were dispersed as expected for a territorial species. Compared with yearling males and with females, older redstart males were observed significantly more frequently during playbacks than predicted by pre-playback relative frequencies. No such sex bias was found for Black-throated Blue Warblers, a species in which age cannot be reliably determined except with hand-held individuals. Diurnal variation in surveyed abundances of both species was relatively minor, but was significantly less pronounced for playback counts than for pre-vocalization counts in Black-throated Blue Warblers. Our results indicate that broadcast territorial advertisement vocalizations provide a powerful tool to study the ecology and distribution of neotropical migrant songbirds in winter.