SEXUAL HABITAT SEGREGATION BY AMERICAN REDSTARTS WINTERING IN JAMAICA- IMPORTANCE OF RESOURCE SEASONALITY

We tested the hypothesis that wintering populations of American Redsta rts (Setophaga ruticilla) segregate into different habitats by sex in response to ecological conditions associated with an extensive dry sea son, which typically develops after migrants arrive in northern Neotro pical sites. Sex-specific distribution and overwinter persistence of r edstarts were quantified at a Jamaican mangrove-scrub ecotone. We also contrasted vegetation structure and food availability in winter terri tories of the two sexes and in both habitats within and between season s. 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-bas ed difference in overwinter persistence on territories. The average ma ngrove territory had a higher canopy and more-open understory, higher relative humidity, and greater insect biomass within a season for seve ral 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 feat ures and food abundances in mangrove habitats, affect winter habitat q uality for nonbreeding redstarts.