Assessing the effects of natural disturbance on a neotropical migrant songbird

Large-scale natural habitat disturbances can play major roles in structurin g the distribution of individuals and ecosystems,and can exert substantial selective pressures. The magnitude of these effects depends on the spatial and temporal scale of the disturbance, as well its frequency, intensity, an d predictability. In January 1998, the worst ice storm in documented Canadi an history struck southern Ontario and Quebec. This storm affected > 10(6) ha of forest, causing widespread damage. One region negatively affected by the storm is home to a large breeding population of Cerulean Warblers, Dend roica cerulea. This population has been studied since 1994, thereby allowin g a unique opportunity to examine the effects of a large-scale natural habi tat disturbance on the reproductive ecology and behavior of this Neotropica l migrant songbird. We addressed two main questions: (1) did Cerulean Warbl er reproductive success change after this habitat disturbance, and (2) did the breeding population exhibit a shift in habitat selection patterns in re sponse to this habitat disturbance? The January 1998 ice storm caused a sig nificant reduction in the amount of forest canopy foliage in our study area the following spring. This was followed by a significant decline in Cerule an Warbler reproductive output in the 1998 breeding season. In 1999, Cerule an Warblers demonstrated a significant increase in territory size and a sig nificant shift in nest-site location patterns; these shifts were accompanie d by a significant increase in reproductive success. The 1999 shifts in ter ritory and nest-site location patterns were effected by the same individual s who were failed breeders in 1998. This suggests that Cerulean Warblers po ssess a degree of plasticity in their habitat affinities, and that this pla sticity rendered the population somewhat resilient to this particular distu rbance.