Usually, birds of a feather flock together -- but in the Amazon, some flocks feature dozens of species of all shapes and colors. A new study singles out one reason why these unusually diverse flocks exist: lookout species that call in alarm when they spot dangerous predators. Researchers have pondered the existence of these mixed-species flocks for decades, especially because of their stability. But scientists did have a few clues. One ubiquitous group of flock members are species whose calls alert their neighbors to the presence of threats like hawks or falcons. To put that idea to the test, the team captured alarm-calling dusky-throated antshrikes (Thamnomanes ardesiacus) from eight mixed-species flocks in southeastern Peru and kept each bird in an aviary for several days. After the team removed the antshrikes, birds in each flock responded in a matter of hours. In three flocks, birds retreated to areas of denser cover at the same vertical level in the forest, while in another the members joined new flocks high in the canopy, another area that affords more cover from predators. Birds in control flocks, where the researchers captured antshrikes but immediately released them, tended to stay out in the open. The results support the idea that alarm-calling species might allow their neighbors to live in dangerous neighborhoods.
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