The lifeless corpse belongs to a crow, and the dark-garbed group congregating nearby is a gathering of its fellow crows, sometimes referred to as a “murder.” That name is particularly apt in this case, as murder is what holds their attention. Their vigilance over a dead crow serves a purpose — one that’s a matter of life and death, according to a new study in the journal Animal Behavior. By sticking close to a crow that was killed, other crows may improve their chances of learning about predators they need to avoid.
Human rituals for dealing with the dead are numerous and varied. But animals in the wild are not widely known to behave in an unusual way when confronting a dead animal of their own species. In fact, the researchers said in the study, “few animals have been reported to show more than a passing interest.” African elephants will touch, groom or otherwise attend to a dead elephant, and scientists have noted similar behavior in bottlenose dolphins, chimpanzees and certain species of jays and magpies, the researchers reported.
And for birds in particular, a growing body of evidence suggests that their interactions with dead members of their own species serve a critical purpose — “to assess danger and trigger anti-predator behaviors,” the scientists said in the study.
Crows are widely recognized as highly intelligent. They can solve puzzles inspired by Aesop’s Fables, and learn how to use tools by watching more experienced crows in action. Studies have shown that crows hold grudges, remembering the faces of humans who mistreated them even after years had passed.
And once you get on the wrong side of a crow, not only are they probably going to remember you, but they’re likely to tell their friends about you, too.
The scientists cited an earlier study showing that American crows gather and act aggressively, behavior known as “mobbing,” in response to audio playback of a crow’s distress call, played near a dead crow. And the crows later avoided the territories where dead crows had been found, even if those locations had plenty of food.
Clearly, crows could learn to be wary of areas where their fellow crows turned up dead. The researchers wanted to know if they would also learn to associate dead crows — and threats to themselves — with specific predators.
The researchers went to great lengths to design the "threats" they used to test the crows. They set up feeding areas for urban wild crows and sent trained volunteers to visit, carrying different objects that were carefully selected to test the crows' alarm responses: taxidermy crows arranged in poses suggesting that they were dead, and taxidermy red-tailed hawks, which prey on crows, posed on a branch as though they were still alive.
Then, volunteers would visit the feeding areas. Sometimes they would carry the "dead" crow, sometimes they would carry the "live" hawk, and sometimes they would carry both at the same time. To make things easier for the researchers (and more surreal for passers-by) the volunteers were masked, eliminating the possibility that variations in their expressions would affect the crows' responses.
The crows reacted by vocally scolding and mobbing the volunteers carrying the "dead" crows, the posed hawks and the two taxidermy birds at the same time. After one of these encounters, the crows also appeared more watchful of the feeding area, taking longer to approach the food.
And the crows also appeared to remember the masks worn by the volunteers who held the dead birds. Even if a mask-wearer only carried a dead crow once, the crows continued to scold that person whenever they appeared, for up to six weeks.
Read more at Discovery News
No comments:
Post a Comment