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Why do many animal migrations follow an annual seasonal cycle?
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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.
Many animal migrations follow an annual seasonal cycle because they are closely integrated into the annual cycle of ecosystems characterized by fluctuating productivity. This behavior allows animals to exploit temporary food surpluses in different regions while avoiding areas where resources become scarce due to seasonal changes.1
The timing of these migrations is governed by a combination of internal and external factors:
- Physiological Preparation: Animals often undergo internal changes, such as fat accumulation and metabolic shifts, regulated by the pituitary gland and hormones. These processes are often triggered by predictable environmental cues like changes in day length (photoperiodism).2
- Ecological Triggers: Because environmental conditions—such as weather, temperature, and food availability—are often irregular, the internal cycle serves to prepare the animal, while specific ecological conditions act as the final trigger for departure.2
- Resource Exploitation: Migration enables species to move between life zones, such as the Arctic and the tropics, ensuring they are present in habitats when productivity is at its peak.1
By following these cycles, migratory species can inhabit areas that would otherwise be untenable during extreme seasons, ensuring their survival and the efficient use of global food resources.13