Winter Ecology and Conservation Implications for the Endangered Migrant Kirtland's Warbler in the Bahamas
During six winters of field studies in the Bahamas, Forest Service scientist Joseph Wunderle found that the endangered Kirtland's Warbler's food resources (fruit and arthropods) typically declined during a winter, but not always consistently due to yearly variation within and between study sites. Despite variation in food availability as driven by rainfall, the proportions of fruit and arthropods in the warbler's diet varied little within a winter or with sex or age class. Site fidelity within and between winters as well as late winter body mass and fat varied by sex (males greater than females) and age class (adults greater than juveniles), consistent with expected outcomes of dominance and experience. But knowledge of only sex and age was insufficient to predict site fidelity in a model-selection framework in the absence of other contributing variables such as food resources and habitat structure. These analyses further indicated that measures of either arthropods or fruits were reliable positive predictors of site fidelity. Birds that shifted between study sites within a winter moved to sites with a higher biomass of fruit and ground arthropods, such that late winter warbler densities were positively related to the biomass of fruits and ground arthropods. Late winter rain had a positive effect on fruit abundance and corrected body mass; corroborating previous Kirtland's Warbler studies that showed carryover effects on the breeding grounds and that survival in the following year was positively correlated with March rainfall in the Bahamas. Given that drought reduces food resources and body condition of the warbler in the Bahamas, which negatively affects its survival and breeding in North America, conservation efforts in the Bahamas archipelago should focus on protecting the least drought-prone early successional habitats with favored fruit species.