Ornithologist Clinton Francis was leading a class field trip along the California coast when students spotted what appeared to be an injured Killdeer. They watched as the striking shorebird aggressively called and held out a contorted wing. When Francis explained that the Killdeer was faking it, using what’s called a broken-wing display to lure predators away from its nest, a student asked a question that seemed simple, but proved challenging to answer: What other species do that?
Francis knew other shorebirds and some doves performed the display, but he wasn’t sure how widespread it was. So, he encouraged enthusiastic students at California Polytechnic State University to find out. “It’s fun to see these projects,” Francis says. “Students get really curious about something they see in the field and really run with it.”
That simple question in 2016 transformed from a senior project to a peer-reviewed study published in March in Proceedings of the Royal Society B. Francis, along with students and colleagues, found nearly 300 species that perform the broken-wing display across the world, upending the long-held idea that this was mainly a shorebird behavior. “That was super surprising to me,” Francis says.
The broken-wing display is just one of the many creative behaviors animals have evolved to avoid becoming a meal. The eastern hognose snake, for example, plays dead when threatened, rolling onto its back and emitting droplets of blood to exaggerate the stunt. Some animals may flush or freeze, like herons and egrets, when an attacker approaches too closely. But evading predators is more complicated during the breeding season, when birds must balance their own survival with preventing the next generation from becoming nugget-size snacks.
Some parents aggressively mob potential attackers to save their chicks: Common Terns, for example, are infamous for their fierce attacks on seabird researchers. Nightjars take a different approach, using camouflage to blend into their surroundings and hide both themselves and their nests. Distraction displays are another set of tools that allow the parent to protect its young and escape at the last second.
These attention-grabbing maneuvers escalate in intensity as the breeding season progresses. “They sort of exist on a continuum,” says Paul Smith, an ornithologist at Environment and Climate Change Canada who has studied shorebirds breeding in the Arctic for almost 25 years. At their simplest, distraction displays might just involve a bird calling to capture an attacker’s attention. Other birds take it a step further, running in a crouched posture away from the nest with its tail between its legs—called a “rodent-run” because it mimics the main prey of some predators—hoping the hungry hunter will follow. And among the most complicated of these behaviors is the broken-wing display, which varies among individuals and species, from the Killdeer’s dramatic performance to a Snowy Plover that remains motionless with outstretched wings.
To identify all birds that use this ploy—not just the well-documented shorebirds—the team of researchers, including co-author and then-undergraduate student Wren Thompson, dove into the literature. “It started with just searching ‘broken-wing display’ and seeing if that was actually an established term,” says Thompson, now a museology graduate student at University of Washington. The researchers painstakingly scanned databases of scientific studies and the Handbook of the Birds of the World, and surveyed nearly 100 ornithologists and birders to track down additional species, which maybe weren’t formally recorded, that they’d witnessed performing the display.
Their year-and-a half-long effort yielded 285 species from 52 families across the world. Only one in five of them turned out to be shorebirds, with ducks, songbirds, and even owls using the broken-wing display. “I was stunned,” Thompson says.
And that could be just the beginning, according to Francis. “There’s a lot of species out there that may very well perform the display that we missed, just because someone hasn’t written it down in English, in a place that we could find it,” he says.
After finding the behavior so widespread, the researchers next asked what causes some birds to perform the display when so many other species don’t. They looked at 16 features, such as body size, breeding latitude, and how well each species conceals its nest. Among their findings, the team discovered that birds breeding at higher latitudes were more likely to perform the display than tropical birds. They also found that species which don’t conceal their nests tend to use the broken-wing trick more often than those with well-hidden nests. The combined results point to a larger force at play: predation risk.
StepsPart
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Put on some gloves to shield yourself from any bacteria the bird may be carrying before attempting to assist a bird with a broken wing. Wearing gloves, gently wrap the bird in a towel to help it relax and stop it from injuring itself any more. After wrapping the bird, put it inside a cardboard box with another towel inside to keep it cozy and safe. It is likely too afraid to eat or drink, so don’t give it food or water. After you’ve placed the bird in a box, give your neighborhood veterinarian a call to get their advice. Try contacting local bird rescues to see if they can take in the bird if they are unable to assist you. Continue reading for additional advice from our Veterinary co-author, such as how to give an injured bird more heat!
The reason why some birds perform the display while so many other species do not was the next question the researchers asked after discovering how common the behavior is. They examined sixteen characteristics, including body mass, breeding latitude, and nest concealment ability of each species. The researchers found that, in comparison to tropical birds, birds breeding at higher latitudes were more likely to put on the show. Additionally, they discovered that, compared to species with well-hidden nests, those without nests typically employ the broken-wing trick more frequently. The aggregate findings indicate a more powerful factor at work: predation risk.
One of the many inventive ways animals have evolved to avoid becoming food is the broken-wing display. When threatened, the eastern hognose snake, for instance, rolls onto its back and spits out droplets of blood to make the act seem more dramatic. When an attacker gets too close, certain animals, like herons and egrets, may flush or freeze. However, during the breeding season, when birds have to balance their own survival with keeping the next generation from becoming nugget-sized snacks, avoiding predators becomes more difficult.
Scholars such as Smith are astute enough to spot the deceit and exercise caution when studying the birds so as not to injure the young or put undue stress on the adults. Those who enjoy the outdoors during breeding season, including birdwatchers, should use similar caution. Finding a bird that is calling loudly and seems to be holding a broken wing is a sign that the nest is close by, but it can also indicate that you are getting too close.
That simple question in 2016 transformed from a senior project to a peer-reviewed study published in March in Proceedings of the Royal Society B. Francis, along with students and colleagues, found nearly 300 species that perform the broken-wing display across the world, upending the long-held idea that this was mainly a shorebird behavior. “That was super surprising to me,” Francis says.
Of course, there are downsides to faking an injury. Although engaging in this behavior helps birds burn some calories, the biggest risk is getting too close to a deadly attacker. Smith states that “occasionally birds do get gobbled up by the predators while doing these distraction displays.” It is simpler and safer for the birds to flee if they are not anchored to a nest.
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