CONTROL MECHANISMS OF THE TIMING OF SPRING MIGRATION IN BIRDS

The question which factors govern the timing of migration in birds has long fascinated researchers. It was initially assumed that avian migration is triggered by the environmental factors such as ambient temperature and food availability. Later lab experiments in various avian species convincingly showed that the timing of spring migration was mainly governed by daylength (photoperiod), being controlled by circannual rhythms. As a result, the concept that environmental factors (air temperature, precipitation, food availability) had no significant impact on the timing of spring migration became generally accepted. However, in the recent decades more and more facts became available showing that the timing of spring migration in many bird species changed significantly. These facts allow to formulate a novel concept of regulation mechanisms of the timing of spring migration which accounts not only for photoperiodic and endogenous control, but also for the already mentioned extrinsic factors. Studies on the endocrine control of spring migratory disposition showed that the features of endocrine mechanisms governing the onset of spring migration depended on species-specific migratory strategies, the stability of environmental conditions in winter quarters, and on migratory routes. It becomes clear which endocrine mechanisms are involved in adjusting the migratory behaviour to variations in local environments. In the recent years, progress has been made in finding genetic mechanisms controlling the timing of spring migration.