We compared growth rates of Black Brant (Branta bernicla nigricans) goslings from two dispersed nesting aggregations to those from the large Tutakoke River Colony on the Yukon-Kuskokwim Delta, Alaska during summers, 1999 and 2000. Approximately 20% of the Black Brant population on the Yukon-Kuskokwim Delta, Alaska nests outside of the four major colonies. Dispersal to these outlying breeding locations is hypothesized as a mechanism by which individuals reduce the negative effects of density dependence associated with major colonies. Growth rates of goslings varied among brood rearing areas both associated with dispersed nesting aggregations (n = 4) and associated with the Tutakoke River Colony (n = 7). Mean mass of goslings, adjusted for age, from brood rearing areas associated with dispersed nesting aggregations ranked sixth, eighth, and ninth of nine brood rearing areas sampled in 1999, and sixth and ninth of nine brood rearing areas sampled in 2000. Mean age-adjusted mass of goslings with the largest mass were 198 and 139 g lighter, respectively, from brood rearing areas associated with a dispersed nesting aggregation than those from brood rearing areas associated with the Tutakoke River colony in 1999 and 2000. Our findings suggest that goslings from dispersed nesting aggregations we sampled are unlikely to have an advantage over goslings from a major colony with respect to survival, adult body size, and recruitment.
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Vol. 120 • No. 4