Extent of double-brooding and seasonal movement of nesting females in a northern population of Wood Thrushes

Accurate estimates of the amount of double-brooding within a population are an important parameter for assessing the population sustainability of fore st birds. In 1998 and 1999, we color-banded adult female Wood Thrushes (Hyl ocichla mustelina) at 70 nests early in the breeding season to assess the f requency of double-brooding in a northern population. We found that double- brooding was a common breeding strategy among Wood Thrushes in southern Ont ario. Forty-seven females fledged first broods and 74% (n = 35) of them ini tiated egg-laying in a subsequent nest. It is possible that at least 87% (n = 41) of the females were double-brooded, based on the evidence of 6 later nests built within 50 m of successful first nests that were depredated or fledged young before their owners could be identified. Other second-brood n ests were probably missed because they were overlooked and because some fem ales moved considerable distances (100-400 m) between nestings. Most birds that failed in their early nesting attempt were not found again on the site , precluding verification of their renesting efforts.