Mechanisms and their Consequences in a Changing World Alexandra Komissarova Abstract Many migratory species are responding to climate change by altering their migration behaviour, however, we know relatively little about the mechanisms by which such changes are accomplished. One way in which climate change could be influencing migration strategies is through its effect on habitat and territory quality. I tested several hypotheses of different mechanisms by which three aspects of territory quality could affect migration decisions in a partially migrant bird, the robin (Erithacus rubecula). I also used a theoretical individual-based modelling approach to investigate the interaction between migration and dispersal strategies within a population and examined its underlying mechanisms. Migration decisions were not significantly affected by summer territory quality, as measured by breeding success and summer vegetation structure. Winter territory quality was, however, found to be a good predictor of migration behaviour, with aspects of winter vegetation such as ground cover appearing particularly important. However, this effect of winter vegetation structure on migration decisions appeared to be largely due to its correlation with food availability. Migration decisions were strongly affected by winter food availability, with provisioning of food greatly increasing the numbers of resident individuals. The results of the theoretical model showed a that high rates of dispersal within a population reduced the average proportion of migrants, with the effect strongly influenced by dispersal cost and to a lesser extent, kin selection. I hope that this work will ultimately improve our ability to predict species’ responses to climate change by adding to our understanding of the mechanisms behind migration decisions, while also providing a more holistic view of migration by placing it in the context of other life history decisions.

Thesis (M.S.) in Wildlife Ecology--University of Maine, 2003. / Includes vita. Includes bibliographical references (leaves 124-136).