If you hear an owl hooting at dusk, don't expect to catch the flute-like song of a Veery nearby. This North American thrush has probably also heard the hoots, and is singing much less to ensure that it does not become an owl's next meal.
Research by Kenneth Schmidt of Texas Tech University and Kara Loeb Belinsky of Arcadia University in the US, published in Springer's journal Behavioral Ecology and Sociobiology, provides insights into just how eavesdropping between predators and prey around dusk may be shaping communication in birds. The study is the first to use the playback of recorded owl vocalization at sunset to study how birds change their behavior when potential predators are heard nearby.
Perching birds are generally more exposed during periods of extended singing. They are less vigilant and their song can often attract the attention of a predator to their fixed location. Despite this risk, dawn and dusk chorusing is a common trait. One such perching bird is the Veery (Catharus fuscescens), a common small brown and white thrush that is most active during the day. Its most common call is a harsh, descending "vee-er", from which the bird gets its name. This particularly vocal bird has a breezy, flute-like song, a pronounced dusk chorus and is often heard singing well after sunset. This behavior could potentially expose the bird to predation.
The study was done on the forested property of the Cary Institute of Ecosystem Studies in Millbrook, New York, where up to three pairs of barred owls live. This owl species is known to be a predator of Veeries. The researchers found that the Veeries reduced their singing patterns for up to 30 minutes after recorded owl sounds were played. The songbirds also displayed fewer extended singing bouts at dusk and stopped singing much earlier in the evening.
"Singing becomes much more risky in the low light of dusk when owls are around," explains Schmidt. "However, by eavesdropping on owls, Veeries can adapt their singing behavior to decrease the risk of predation."
Schmidt adds that the study of the avian dusk chorus has been largely ignored relative to the more well-researched dawn chorus. "Further studies of dusk chorus singing may reveal how the risk of being attacked by predators has contributed to the evolution of singing behavior at dusk," he believes.
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More information: Schmidt, K.A., Belinsky, K.L. (2013) Voices in the dark: predation risk by owls influence dusk singing in a diurnal passerine, Behavioral Ecology and Sociobiology. DOI 10.1007/s00265-013-1593-7