Circannual Rhythms in the Control of Avian Migrations

Abstract

Publisher Summary The chapter discusses some functional aspects of circannual rhythms in migratory birds and summarizes the results that have accumulated over the past few years, indicating a fundamental involvement of endogenous circannual programs in the control of various aspects of migratory behavior, particularly in long-distance migrants. Subsequent investigations have justified this approach as they have revealed that: (1) endogenous circannual factors are the primary cause for the onset of spring migration in birds with an equatorial wintering area, and that species or population differences in the timing of migrations are partly the result of differences in circannual organization; (2) genetically fixed circannual programs can determine the overall amount and the time course of a first fall migration, possibly to the extent that they even determine migratory distance; and (3) a circannual clock mechanism may be involved in shifting the migratory direction in the course of the year.