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Breeding dispersions and site fidelity of American redstarts (Setophaga ruticilla)

We relate features of the breeding dispersions and site fidelity of American redstarts (Setophaga ruticilla) to breeding success and interpret the findings in terms of sexual selection. One-year-old male redstarts show delayed plumage maturation, making male dispersions particularly easy to appreciate. In our study site in New Brunswick, Canada, older males usually arrived early each breeding season and gathered in contiguous territories or neighborhoods, while subadult males arrived later and settled peripherally to the adults. Subadult males constituted about 40% of the male population, on average, yet only 5% of banded nestlings returned to the natal breeding ground. Also, newly adult males, 2 years old or more, constituted about 15% of all males. Nearly 50% of adult males returned, twice the return rate of subadults. Among returns, older males returned more often to the same territory than did those that were subadult the previous year. Regardless of age, returns of males in a subsequent year were predicted more by the duration of their stay on the breeding territory than reproductive success. Males outnumbered females. Females returned less often than their mates, but more often if they had fledged young. Females rarely returned to the same mate or territory, but often returned to the same vicinity. The subadult males seem to represent a special dispersive phase of the life history. The evidence indicates strong competition among males for territories and females, older males being more often successful in both circumstances.