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Winter 2011

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

February 1, 2011

Mixed-species foraging: Birds of different feathers flock together

Mixed-species foraging: tufted titmouse, brown creeper and downy woodpecker

In the winter woods, you may suddenly find yourself surrounded by a slow-moving gang of birds, a hunting party of several small species foraging for food together.

Tufted titmice and Carolina chickadees are ringleaders of the bunch, which may also include kinglets, brown creepers, downy woodpeckers and white-breasted nuthatches.

Mixed-species foraging is less common when food is abundant, which supports the notion that the behavior increases feeding efficiency. In such flocks, birds can learn about food sources from other species, and the foraging is less competitive than in a flock made up of only one species.

With the mixed flock's variety of eyes and ears on alert, the birds may be safer from predators. They can spend more time searching for food and less time watching their backs.

Woodpeckers and nuthatches clearly benefit from the coalition. Outside the mixed flock they are more vigilant and less likely to leave their comfort zones, resulting in their eating less and suffering higher mortality rates.

But not everybody on the team is a winner: Chickadees pay a price when they join such flocks. They fare better when foraging on their own, because in mixed flocks titmice steal food from them.

SOURCES: Ecology, Stanford University, Animal Behavior

Mixed-species foraging: Carolina chickadee, white=breasted nuthatch and golden-crowned kinglet.