Predator-specific alerts allow multiple species to survive by providing an early warning system.

Edit Hook

The sound of birds singing in a woodland can seem like a confusing jumble of trills, whistles, and chirps. But there’s a lot of communication going on. Scientists found that birds and mammals broadcast warnings about nearby predators, and different species (including mammals) understand each other’s messages. They can even share information on what kind and size of predator is around, and what it’s doing.

Black-capped chickadees are tiny black and white birds who live in forests. They’re best known for their “chickadee dee dee” calls. These and some other calls keep birds in contact with each other or let each other know where to find food. Less noticed by humans is a very quiet, high-pitched “seet” call. They use this call to warn others that there’s a hawk or owl flying nearby. 

Chickadees also have another call when they see a perched hawk or owl. It’s a louder and longer  version of its  usual “chickadee dee dee” call. This altered call draws in other birds to “mob” the predator. The more dangerous the predator is to the chickadees, the more times they say “dee”. For example, the tiny northern pygmy-owl, who eats a lot of chickadees, gets more “dee” calls. The bigger great horned owl is less of a threat and so the birds make fewer “dees”. The harsh “chickadee dee dee” means the chickadee sees a hawk or owl and needs other nearby birds to mob the predator until it flies away. [Watch video of hawk being mobbed by chickadees.]

The “seet” call has a different purpose. Because it’s so quiet and high-pitched, it’s hard for a predatory bird to hear. That means it’s a safer call for a chickadee to make compared to the deeper, louder “chickadee dee dee.” The “seet” call warns other chickadees to hide when a hawk or owl is flying nearby. Like an early warning system, the alert can spread through a forest from one bird to another faster than the hawk can fly. By the time the predator arrives, the birds are safely in hiding. 

Other species can also ‘listen in’ on the chickadees’ warnings, including nuthatches, jays, squirrels, and chipmunks. Birds in other countries also react to the “seet” call even if  chickadees don’t live in the area. Scientists have played a recording of the chickadee’s “seet” call all over the world, and other birds understood it and took cover.

The early warning system goes beyond directly saving birds and mammals from predators. This cooperation allows them to spend less time watching for predators and more time getting the food they need to survive.

To listen to a chickadee “seet” call, listen to the last one on this page.

Edit Summary

References

“In addition to being one of the most subtle and sophisticated signaling systems yet discovered, this system is unusual in that it combines aspects of both referential and risk-based antipredator vocalization systems. To denote the presence of a rapidly moving predator (e.g., raptor in flight), chickadees produce a “seet” alarm call. When they encounter a stationary predator (e.g., perched raptor), they use the “chick-a-dee” mobbing call. These two vocalizations appear to be functionally referential to the type of predator encounter (i.e., each denotes a specific type of encounter). In addition, we have shown that subtle variation in the “chick-a- dee” mobbing call reflects the size of a specific predator, a characteristic of a risk-based system. Thus, chickadees convey information about predators at two different levels: A coarse level of encoding (“seet” or “chick- a-dee”) signifies the type of predator encounter, and a fine level of encoding (variants of “chick-a-dee”) signifies the degree of danger presented by that specific predator encounter.” (Templeton et al. 2005:1937)

Journal article
Templeton CN, Greene E, Davis K. 2005. Allometry of alarm calls: black-capped chickadees encode information about predator size. Science 308:1934-1937. ScienceTempleton CN, Greene E, Davis K

Journal article
Templeton CN, Greene E. 2007. Nuthatches eavesdrop on variations in heterospecific chickadee mobbing alarm calls. PNAS 104(13):5479-5482.PNASTempleton CN, Greene E

Journal article
Billings AC, Greene E, Jensen MDLL. 2015. Are chickadees good listeners? Antipredator responses to raptor vocalizations. Animal Behaviour 110:1-8.Animal BehaviourBillings AC, Greene E, Jensen MDLL

Newspaper article
Solomon C. 2015. When birds squawk, other species seem to listen. The New York Times. The New York TimesSolomon C

Web page
Joyce C, McQuay B. 2015. Squirrels mimic bird alarms to foil enemy. Close Listening: Coding Nature Through Sound. NPR. Close Listening: Coding Nature Through Sound on NPRJoyce C, McQuay B

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