For the first time, female dark-eyed juncos have been found to burst into song in the wild. Although many female tropical birds sing, singing females are rare among northern, temperate songbirds. However, the behaviour is now becoming more common, and climate change may mean it becomes even more widespread.
Dustin Reichard of Ohio Wesleyan University knew that female dark-eyed juncos (Junco hyemalis) sometimes sang in captivity, but only after being injected with testosterone. To find out if they sang in the wild, he and his colleagues goaded them by placing a live, caged female in their territories. The researchers also played recordings of a soft trill that females make when they are receptive to mating.
In all, 17 females, along with 25 males, interacted with the caged females. Half the females dived and lunged at them, and a minority also performed aggressive tail-spreads not normally seen in females. Three of the females sang songs similar to those of males.
“The context in which the songs were observed – responding to a female intruder – suggests these songs have an aggressive, territorial function,” says Reichard. “But we can’t say whether female song is specific to female intruders without also measuring their response to male intruders.”
The females also reacted badly to attempts by males to woo the intruder female, both with song and other courtship behaviours such as puffing up their feathers and spreading their tails. Dark-eyed juncos are monogamous, and the females sought to keep their mates faithful by aggressively chasing them away from the rival female.
“The results provide some of the first evidence that female song can be rapidly regained in a songbird species,” says Jordan Price at St Mary’s College of Maryland, who has documented female songs in New World blackbirds.
A key factor may be a change in the birds’ lifestyle. “The junco population we studied actually stopped migrating about 35 years ago and became year-round residents of San Diego, California,” says Reichard. This means the females must defend territories all year. “It may suggest that if a species loses its migratory lifestyle, they might gain female song,” he says.
“Recent studies are showing that female singing is much more common than previously thought, especially in birds that are non-migratory and in which males and females defend territories all year round,” says Price. Such behaviour is prevalent in the tropics, which may explain why female birdsong is common there. “But in temperate-zone songbirds, the widespread belief is that males sing and females don’t.”
As climate change raises temperatures, tropical birds may expand their ranges into what are now temperate zones, Reichard says. “Then we may see more singing females in the higher latitudes.”