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Winter habitat quality and year-round population processes: Insights from individual upgrade experiments with a long-distance migratory bird.
Studds, Colin*,1, 2, Marra, Peter1, 1 Smithsonian Environmental Research Center, Edgewater, MD2 University of Maryland, College Park, MD
ABSTRACT- Evidence is accumulating that habitat quality on non-breeding grounds is critical in structuring the annual population dynamics of long-distance migratory birds. American redstarts (Setophaga ruticilla) overwintering in Jamaica provide an excellent system to experimentally test this hypothesis. Behaviorally dominant, primarily male redstarts exclude females and younger males from high quality black mangrove forest, forcing them to occupy sub-optimal second-growth scrub habitat. In 2002 and 2003, we experimentally upgraded redstarts to higher quality habitat by permanently removing birds from adjacent mangrove forest, allowing individuals from scrub to colonize vacated territories. Relative to control birds that overwintered exclusively in second-growth scrub, redstarts upgraded to mangrove forest maintained body mass from winter to spring, departed earlier for spring migration, and had higher apparent annual survival. Our results provide the first experimental evidence of the importance of non-breeding season habitat quality to overall population-level processes. Changes in physical condition associated with winter habitat quality can carry over into subsequent phases of the annual cycle, potentially affecting population dynamics.
Key words: non-breeding season, seasonal interactions, habitat quality, removal experiments