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Why do migratory birds build up fat reserves before migration?

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Two wild horses graze on tall grass in the open prairie of Theodore Roosevelt National Park, with rolling badlands visible in the background. — Feeding behaviour Wild horses graze in the Badlands of North Dakota.

Migratory birds accumulate fat reserves before migration to provide the essential energy required for their long-distance journeys. This process is part of a broader shift in metabolic patterns controlled by the endocrine system, particularly the pituitary gland.12

As day length changes, the pituitary gland secretes hormones that trigger physiological preparations for migration. In the lead-up to the migration season, birds experience an increase in food consumption, which facilitates the storage of fat in their body tissues. These fat deposits serve as a vital fuel source, allowing birds to sustain the high energy demands of flight. This physiological preparation is a highly regulated part of the bird's annual cycle, ensuring they have the necessary resources to navigate successfully between breeding and wintering grounds.12