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How does changing day length affect migratory birds in spring and autumn?
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Migration
A herd of common wildebeest (Connochaetes taurinus) migrating across a dusty savanna in Africa. The animal is a keystone species (i.e., a species with a disproportionately large effect on its biological community) in plains and acacia savanna ecosystems from southeastern Africa to central Kenya.
Changes in day length, a phenomenon known as photoperiodism, serve as a critical environmental cue that influences the migration of birds by interacting with their endocrine systems.123
The pituitary gland acts as a command center, responding to these seasonal light variations to prepare birds for their journey.13
- Spring: As day length increases, the pituitary gland accelerates physiological preparations, such as gonadal development and metabolic adjustments, to ready the bird for the breeding season and migration.3
- Autumn: As day length decreases, the pituitary gland triggers hormonal changes that lead to the accumulation of fat in body tissues, providing the essential energy reserves required for long-distance flight.13
While these light-induced physiological changes are highly predictable, they do not act alone. The pituitary serves to prepare the bird, but the actual initiation of migration often requires favorable ecological conditions, such as temperature, barometric pressure, and food availability, which can vary significantly from year to year.3