Changes in the phenology of breeding and migration in relation to global climate change

The timing of life history events is often critical for the fitness of organisms. Among birds, the timing of events at the start of the breeding season can, for example, determine an individual’s chance of obtaining breeding territory and of achieving a level of reproductive success. The timing of migration and egg-laying can be affected by weather conditions, and it has been predicted that climate change could thus have a major impact. Data from a variety of sources strongly suggests that the timing of migration and nesting have already been affected by climate change, and provide some of the strongest early signals of likely impacts from the relatively moderate climate change that has occurred to date. We review information from intensive study sites and extensively gathered data to draw out general patterns, and then briefly consider the potential consequences of such changes for birds.