Demography, gene flow, and nest predatory behavior of the common raven (Corvus corax) in a temperate rainforest.

摘要

I studied a population of ravens on Washington State's Olympic Peninsula by conducting a behavioral experiment, quantifying habitat-specific demography, and analyzing gene flow. For my behavioral experiment, I tested the hypothesis that nest patch structure, local raven abundance, landscape structure, and the occurrence of food bonanzas affect the survival of artificial passerine nests. Raven abundance and experimental food bonanzas were associated with increased nest predation by ravens at every scale of analysis. Increased forest structure was related to decreased risk of raven nest predation at the two smallest scales of analysis. There was no additional concealment effect of mature forest beyond the 100 m distance neighborhood, thus suggesting the scale ( 100 m) at which ravens were capable of finding nests in mature forests. Clearcuts and high-contrast edges were also associated with nest predation, while the density of anthropogenic land cover and mature forest at scales > 100 m were not. My investigation of habitat-specific demography revealed no differences in survival between the sexes, but adults maintained higher survival rates than nonbreeders. Adults displayed strong site fidelity to their territories, while nonbreeders moved extensively. Both adults and nonbreeder home ranges contained similar proportions of resources, but resource use varied between social classes. Raven use of mature forests and anthropogenic land use was positively associated with survival. Adult use of clearcuts and patchy areas contributed to increased reproduction, but the use of clearcuts along with the use of roads was negatively associated with survival. For my study of raven gene flow, I tested the hypothesis that divergent mtDNA lineages of the Common Raven represent uniquely adapted, cryptic lineages. I failed to reject the null hypothesis that mate pairings were random with respect to mtDNA clades, and observed no differences in reproduction between assortative and non-assortatively mated pairs. I found no differences in survival or resource use between clades. There were no differences in morphological or behavioral characters between mtDNA clades. These results suggested there are no barriers to gene flow between mtDNA clades. Hence, in these birds, phylogeographic structure in mtDNA is a reflection of historical isolation rather than adaptive divergence.