Birds learn what danger sounds like

It may not be polite to eavesdrop, but sometimes, listening in on others’ conversations can provide valuable information. And in this way, humans are like most other species in the animal world, where eavesdropping is a common way of gathering information about potential dangers.

Because alarm calls can vary from species to species, scientists have assumed that eavesdropping on these calls of “danger!” requires some kind of learning. Evidence of that learning has been scant, though. The only study to look at this topic tested five golden-mantled ground squirrels and found that the animals may have learned to recognize previously unknown alarm calls. But the experiment couldn’t rule out other explanations for the squirrels’ behavior, such as that the animals had simply become more wary in general.

So Robert Magrath and colleagues at Australian National University in Canberra turned to small Australian birds called superb fairy-wrens. In the wild, these birds will flee to safety when they hear unfamiliar sounds that sound like their own alarm calls, but not when they hear alarm calls that sound different from their own. There’s an exception, though: They’ll take to cover in response to the alarm calls of other species that are common where they live. That suggests the birds learn to recognize those calls.

In the lab, the team played the alarm call from a thornbill or a synthetic alarm call for 10 fairy-wrens. The birds didn’t respond to the noise. Then the birds went through two days of training in which the alarm call was played as a mock predator glided overhead. Another group of birds heard the calls but there was no pretend predator.

On day three, the researchers played the calls again, but without the faux-predator above any of the birds. Eight of the 10 birds that had been exposed to the predator in the previous days fled. None of the others, though, took off when they heard the calls. That showed that the fairy-wrens had learned to associate the previously unfamiliar alarm calls with danger, the researchers report in the August 3 Current Biology.

The team had created their own alarm call, one in which notes increased in tempo and amplitude, because in some species such “looming” sounds, whether familiar or not, can prompt an animal to come to attention or flee. But fairy-wrens that heard that sound without having seen a predator didn’t react, reinforcing the conclusion that the birds were learning.

If birds or other animals can indeed learn the importance of eavesdropping, then this might be something that could be incorporated into conservation programs, the researchers say. In many programs, animals are raised in captivity so they can later be released into the wild to booster populations or establish new ones. These animals are often taught key skills to increase their chances of survival, such as how to recognize a predator. It might be just as useful to teach them how to recognize the alarm calls of other species so they know to flee before ever catching a glimpse of something dangerous.