Male songbirds sing. Females rarely do. At least that’s what we thought for centuries. But now, researchers employing dummies that resemble hawks and snakes reveal that female blue tits sing too. They likely do it to tell predators that they see them and are prepared to flee, according to findings published in the July issue of the Journal of Ornithology.
Males often sing to defend their territory and to court mates. Female songbirds have traditionally been thought of as the mostly mute sex, and only in recent decades have researchers found many exceptions. In the tropics and the subtropics, female songs are often heard in duetting species. In Europe, female blue tits (Cyanistes caeruleus), for example, vocalize in a range of scenarios. While alarm-vocalizations are well studied in both sexes, this behavior hasn’t been observed in female songbirds.
To test how female blue tits respond in danger situations, a team led by Katharina Mahr from the University of Veterinary Medicine in Vienna placed either a stuffed dummy of a sparrow hawk or a rubber Aesculapian snake on a branch near 20 nest boxes in Viennese forests. They found that blue tit females sing in the context of high predation risk. They vocalized during simulated hawk attacks, but not with lurking snakes. That’s likely because sparrow hawks typically attack adult and young birds, while snakes are a bigger threat to nestlings, and they can also be driven away more easily.
The researchers found no support for female singing as a distress call for alerting males: In several cases, the pair sang together in the presence of predators, encouraging each other and strengthening the pair bond. Additionally, the female song strongly resembles that of the male. For a species that has drably-colored, camouflaged females and chicks compared to males, drawing attention with singing seems counterintuitive. It’s possible that singing is just their body’s natural response to a very stressful situation, or it could be a pursuit-deterrent signal for aerial predators. "The animals may be indicating a heightened ability to escape,” Herbert Hoi, also of the University of Veterinary Medicine, explained in a statement. “They show the predator that they have seen it and can flee at any time.” It’s the female’s way of saying “step off” to raptors.