Birds don’t like to fight for food —

Bar-tailed_Godwit_migration route

Why have some birds opted for a taxing life of constant migration — seeking out temperate climates to feed as winter arrives, only to return months later to breed?

Seemingly paradoxically, the behavior is driven by a quest for energy efficiency, a study said. Migrating birds, researchers found, gain more energy from whatever is on the destination menu than they expend getting there and back, or could find without making the trek. Why don’t they just stay in the warm place? Because there is too much competition for food with other species, said the study published in the journal Nature Ecology & Evolution.

Instead, they return to their cold, northern hemisphere home where they don’t have to fight others for the food.

The work “provides strong support for the hypothesis that birds distribute themselves in an optional way in terms of energy,” study co-author Marius Somveille of University of Oxford’s zoology department said.

The uneven distribution of biodiversity on Earth is one of the most general and puzzling patterns in ecology. Many hypotheses have been proposed to explain it, based on evolutionary processes or on constraints related to geography and energy. However, previous studies investigating these hypotheses have been largely descriptive due to the logistical difficulties of conducting controlled experiments on such large geographical scales.

In this case scientists have used bird migration—the seasonal redistribution of approximately 15% of bird species across the world—as a natural experiment for testing the species–energy relationship, the hypothesis that animal diversity is driven by energetic constraints.

Scientists developed a mechanistic model of bird distributions across the world, and across seasons, based on simple ecological and energetic principles. Using this model, they showed that bird species distributions optimize the balance between energy acquisition and energy expenditure while taking into account competition with other species. These findings support, and provide a mechanistic explanation for, the species–energy relationship. The findings also provide a general explanation of migration as a mechanism that allows birds to optimize their energy budget in the face of seasonality and competition. Scientists claim their mechanistic model provides a tool for predicting how ecosystems will respond to global anthropogenic change. (Times of India; Nature Ecology & Evolution)

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