Evidence for Flexibility and Constraint in Migration Systems

The changes in global climate, vegetation zones and sea level must have resulted in changes in the routes taken by migratory species. I consider whether populations are likely to be able to adapt to the accelerating change resulting from modification of the global environment. I summarise 43 cases in which birds have changed their migration routes in historical times. I also summarise 14 cases in which routes seem sub optimal, for example, species have spread from one continent to another but have persisted in using the migration route normally associated with the previous continent. Whether a particular migratory species can respond to global environmental change is likely to depend upon the details of the genetic or cultural system and this may be difficult to predict.