Orientation in birds. Spatiotemporal programmes and genetics of orientation.

A number of migratory bird species have endogenous annual rhythms that regulate the entire annual cycle, including migration. Moreover, captive migrants display inherited migrational activity; this could theoretically also be used by free-living migrants as a time programme for migration. Finally, this heritable migrational activity is oriented in a seasonally appropriate direction, even in naive birds. These characteristics should enable inexperienced migrants isolated from contact with experienced conspecifics, to utilize a heritable vector-navigation programme to migrate from the breeding grounds to the winter quarters. That is, migrants should reach goal areas they have never experienced by migrating in programmed directions, for as long a period as the genetically fixed time programme for migrational activity induces them to do so. The time course of migration, as established by trapping stations, theoretical influences of environmental variables on migration programmes, and also compensatory behaviour and backup measures, are discussed. The present evidence supports the view that a large number of migrants are essentially brought to their wintering areas by vector-navigation systems.