Carry-over effects in wood thrush (Hylocichla mustelina): Linking reproduction to moult.

摘要

Long distance migration of songbirds between their wintering and breeding grounds can be challenging to study. Recent research has begun to consider the interaction or 'carry-over effects' between different periods in a migratory songbird's annual cycle. Multiple brooding is a common reproductive tactic in songbirds, however, little is known about the causes and consequences of having more than one brood in a season. I studied the causes and consequences of double brooding in the Wood Thrush, Hylocichla mustelina. Double brooding was found to increase annual fecundity 4-fold, but double brooding was primarily constrained by high nest failure rates. Birds that double brooded delayed the start of moult by up to 3 weeks and several birds did not initiate moult until late August. I propose that some of these birds may undergo a moult-migration tactic due to breeding season time constraints.;I evaluated the possibility that Wood Thrush undergo a moult-migration tactic by measuring stable hydrogen isotopes (deltaD) in flight feathers and examining moult patterns. deltaD show continent-wide precipitation patterns, and, thus can be used to approximate a rough geographic location of where a particular feather was grown. In 2008, I collected flight feather samples from returning and moulting birds and conducted stable hydrogen isotopes analysis on those feathers. There was variation in the deltaDf values of feathers known to have grown on the breeding grounds. Based on feather isotope analysis 33% of Wood Thrush adopted a moult migration strategy.;My research demonstrates that, while double brooding is highly effective in increasing reproductive output there are carry-over effects into other periods of the annual cycle (e.g. moult). When using 8D it is important to recognize that moult-migration may occur and caution should be taken when determining what feathers to sample.