(CN) — Researchers have found an unusual behavior in the male superb lyrebirds of southeastern Australia: during courtship and mating, males will imitate the cacophonic sound of a panicked “mobbing flock” of birds, a call they typically deploy when a predator is afoot.
“Our paper shows that male superb lyrebirds regularly create a remarkable acoustic illusion of a flock of mobbing birds and, in so doing, create a complex but potent cue of a hidden predator,” said Anastasia Dalziell, lead author of a study published Thursday in the journal Current Biology, in a statement.
Male superb lyrebirds are large, talented songbirds. Many birds can copy others’ songs and certain other noises, but these lyrebirds are masters of mimicry who boast a wide repertoire that includes the sounds of camera shutters, car alarms and even chainsaws. Lady lyrebirds are similarly prone to crooning, though the extent of their vocal range is not as well documented.
The 16 feathers of the males’ wispy tails can grow as long as 28 inches. The two outermost feathers curl in an ‘S’ shape and together resemble the species’ eponymous instrument. Gray-brown with buff-colored outer wings, male superb lyrebirds are more ornate than their female counterparts, who are darker brown and have shorter tails.
Dalziell, a postdoctoral researcher at Australia’s University of Wollongong and a Cornell Lab of Ornithology associate, had set out to study a recital song male superb lyrebirds are known to repeat when she and her colleagues observed an unusual behavior: at the end of each mating dance display, the male lyrebird would mimic the sound of a mixed-species flock of birds ringing the alarm that a predator is near.
“That seemed remarkable — indeed it seemed absurd,” Dalziell said. “We gradually realized that mimicking a mobbing flock during copulation seemed to be the rule for lyrebirds.”
The scientists noted two conditions for the bizarre choice of song.
“Astonishingly, males only mimic a mobbing flock in two contexts: when a potential mate tries to leave a displaying male without copulating, or during copulation itself. These two moments are key to male reproductive success, suggesting that mimicking a mobbing flock is a crucial sexual behavior for males,” Dalziell said.
Dalziell noted that it is difficult to observe lyrebirds’ mating behavior, but she and her fellow researchers managed to produce video recordings of their copulation.
“It was such a strange and complex behavior that we thought that we really needed audio-video footage to show everyone, and we were lucky enough to eventually film several events,” she said.
In a North American backyard, you might hear a blue jay mimic the call of a red-shouldered hawk to scare other birds away from food sources. The purpose is clear: to scare away their competitors. In the paper, the researchers note that the males’ imitation is so accurate that it can startle other species into fleeing.
So why might the male lyrebirds prompt a similar, fear-inducing reaction in a mate during courtship? The study’s authors suggest that the call may be a deceptive “sensory trap” that fools female birds into sticking around for copulation.
“It’s a bit like saying, ‘Baby, it’s dangerous out there. Stay here with me,’” Dalziell said.
The findings complicate the traditional story that ornithologists tell about birdsong’s role in courtship.
“In contrast, our findings provide evidence that complex learned vocalizations can function as deceptive mimicry, most likely a sensory trap, promoting the evolution of elaborate avian vocalizations via sexually antagonistic co-evolution,” the scientists conclude in their paper. “Our study thus provides evidence for a new functional hypothesis for the avian vocal signals we call ‘song’ that does not rely solely on the usual explanations of male-male competition or female choice.”
Dalziell notes that the team’s work with these Australian songbirds isn’t finished. Another odd quirk of superb lyrebird behavior the group noticed is that males will hold their wings over their mate’s head during copulation.
“Are males ‘blindfolding’ females to prevent females from detecting the male’s deception?” she asks, suggesting a potential avenue for future research.