Eavesdropping Nuthatches Understand Chickadees

Red-breasted nuthatches appear to have learned the language of black-capped chickadees. Nuthatches interpret the type of chickadee alarm and can identify what sort of predator poses a threat.

Chickadee calls carry a great deal of meaning to other members of the species but to the human ear, chickadee alert calls sound very similar. However, when a chickadee sees a predator, it makes a soft "seet" for a flying hawk, owl or falcon, or a loud "chick-a-dee-dee-dee" for a perched predator.

Nuthatches have learned to tell if the chickadees are threatened by pygmy owls, which pose a serious threat to small birds, or by much the much larger great horned owls, which rarely attack small birds.

"In this case the nuthatch is able to discriminate the information in this call," said Christopher Templeton, a doctoral candidate at the University of Washington in Seattle.

Templeton and Erick Greene made the discovery after placing speakers at the base of trees in areas frequented by nuthatches and playing recordings of chickadee warnings for both types of owls. The nuthatches became significantly more agitated when they heard recordings of warning calls for pygmy owls, approaching the tree where the speaker was placed to "mob" the predator. Mobbing behavior is a defensive behavior in birds that helps to drive the predator away so it cannot launch a surprise attack.

"For the chickadee calls that signalled a pygmy owl, nuthatches mobbed the speaker more intensely by approaching closer, vocalizing more and spending more time mobbing than during playback of chickadee calls signalling a great horned owl," said Templeton.

Templeton says the nuthatches probably discriminate fine-scaled features in the "chick-a-dee-dee-dee" call such as the number of harmonics in the "dee" notes, or the length and timing of different syllables. "The most important thing our study shows is just how much goes on in nature that we aren't aware of," he said.

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