Climate Change & Migratory Songbirds
Earlier lay dates in birds is one of the most widely-reported responses of wildlife to climate change. We know relatively little, however, about the possible fitness effects of this change in breeding phenology. Most studies of the effects of advancing lay date on the fitness of birds have been carried out in a few European species (e.g., the Pied Flycatcher and Great Tit), which exhibit climate-linked fitness declines associated with increasing asynchrony with their prey.
Based on these European studies, the inference is sometimes made that we might observe climate-linked fitness declines in other species as warming trends continue. However, fitness and population responses to warming springs are almost certain to vary among species that differ in environment, ecology, and life history traits.
Together with researchers from other institutions [Mike Webster (Cornell University), Evan Cooch (Cornell University), Scott Sillett (Smithsonian Conservation Biology Institution), Sara Kaiser (Cornell University), Dick Holmes (Dartmouth College), Nina Lany (Dartmouth College), and Nicholas Rodenhouse (Wellesley College)], we have been examining the phenological, fitness, and population responses to climate change of a Nearctic - Neotropical migratory songbird, the black-throated blue warbler (Setophaga caerulescens), using a long-term dataset from the Hubbard Brook Experimental Forest, New Hampshire. Results to date suggest that—unlike the European model taxa—Black-throated Blue Warblers might actually derive a fitness advantage from warmer springs. However, our modeling efforts suggest that these fecundity gains might not translate into population gains, because warm springs are also linked to lower apparent survival of adult birds. Higher fecundity and lower survival might lead to a net neutral effect of climate change on population dynamics.