Why would a bird perform a particularly conspicuous display in response to a predator’s call? This strange behavior seems like a recipe for disaster, since it probably alerts the predator to the bird’s presence. But for a species of fairy wren, it’s actually a way for males to get females’ attention, according to a new study in Behavioral Ecology.

The study’s authors set out to determine why male splendid fairy wrens (Malurus splendens) tend to sing a particular melody called a “Type II song” just after gray butcherbirds (Cracticus torquatus) vocalize. Butcherbirds are one of the main predators of fairy wrens. Fairy wren males “hitchhike” their responses so closely on the end of the butcherbird’s call that it sounds almost like a duet. Previous studies suggest that the call is some sort of signal to other fairy wrens—not to the predator. The researchers investigated two possibilities about why fairy wrens might perform this odd behavior.

First, Type II songs might be an “honest signal” to potential mates, since only high-quality males would be able to attract that kind of attention from a predator and live to see another day. This signal would reliably show females which males would be the best mates. The second possibility is that when female fairy wrens hear a butcherbird call, they go on high alert and are particularly tuned in to their environment. By singing just after the butcherbird vocalizes, a male can be sure that females are paying attention and will hear their song.

To figure out what was going on, the researchers performed playback experiments to a group of fairy wrens in Southern Australia. First, they played butcherbird calls to 90 male fairy wrens and listened to hear whether the male sang a Type II song in response or not. However, the male’s likelihood to sing had nothing to do with his age, social status, or body condition. This suggests that the birds aren’t using Type II songs as a type of honest signal to communicate their quality to females.

Then the researchers directed their playbacks to the females. They played either a solo butcherbird call, a solo Type II song, or a butcherbird call followed by a Type II song, and recorded the ladies’ reactions. Females sang back to males at a much higher rate if Type II songs were preceded by a butcherbird call, suggesting that the predator call does increase attentiveness. Furthermore, when butcherbird playbacks occurred, males sometimes turned to females and performed visual displays such as the interestingly-named “sea horse flight,” suggesting that the predator’s call stimulates courtship behavior.

This evidence all points to the idea that fairy wrens use the butcherbird’s call as a type of alerting signal. Once females know there’s a predator around, they become attentive and aware. Clever males use this alertness to their advantage to make sure potential mates hear their song.

Interestingly, Type II hitchhiking almost always follows a butcherbird call, rather than the song of any other predator. This may be because—as long as the fairy wrens are paying attention—butcherbirds are unlikely to snatch them. Butcherbirds dive to the ground to capture their prey, so alert fairy wrens that have retreated to the bushes aren’t in too much danger. While this type of behavior is a risk, it’s a calculated one.

The article’s press release, entitled Australian Birds Attract Mates With "Scary Movie Effect" makes the requisite anthropomorphism, claiming that this behavior is like “using a horror film to bring your date closer.” Guys all know that scary movies and roller coasters are great first-date ideas, but the truth is that we just don’t know enough about this process in other species yet; the mechanism behind this behavior in fairy wrens may be completely different.

Behavioral Ecology, 2010. DOI: 10.1093/beheco/arq15 (About DOIs).

Listing image by Richard Taylor