Sexual Habitat Segregation by American Redstarts Wintering in Jamaica: Importance of Resource Seasonality

ABsnTRCr.-We tested the hypothesis that wintering populations of American Redstarts (Setophaga ruticilla) segregate into different habitats by sex in response to ecological conditions associated with an extensive dry season, which typically develops after migrants arrive in northern Neotropical sites. Sex-specific distribution and overwinter persistence of redstarts were quantified at a Jamaican mangrove-scrub ecotone. We also contrasted vegetation structure and food availability in winter territories of the two sexes and in both habitats within and between seasons. Male and female redstarts were significantly segregated by habitat, with males holding territories in mangroves and females predominantly in contiguous scrub habitat. However, we found no significant sex-based difference in overwinter persistence on territories. The average mangrove territory had a higher canopy and more-open understory, higher relative humidity, and greater insect biomass within a season for several insect orders important in redstart diets. Canopy (leaf) cover and abundances of several insect taxa remained more constant over the dry season in mangrove than in scrub habitat. We argue that these between-habitat differences, especially seasonal stability of vegetation features and food abundances in mangrove habitats, affect winter habitat quality for nonbreeding redstarts. Received 3 March 1993, accepted 31 May 1993.