Birds may be bilingual, trilingual or better, suggest new findings that birds in the wild can learn the vocalizations of other species.
The discovery not only proves that birds eavesdrop on what other birds are saying, but it also provides some of the strongest evidence to date that birds can learn "foreign" calls, as opposed to just confusing similar sounds with their own.
While humans may learn a foreign language for work or pleasure, the skill can mean life or death for little songbirds that, according to the study, pay attention to the alarm calls sounded by other birds when a predator, such as a hawk, approaches.
"It's tricky to know what goes on inside another species' head," lead author Robert Magrath told Discovery News. "At one extreme, perhaps they are labeling, such as 'flying hawk approaching at 10m!' or 'hawk flying by in the distance,' or 'predator on the ground,' etc."
Magrath, an associate professor of botany and zoology at the Australian National University, added that the vocalizations could be prompted by anxiety too.
"The best evidence is that both labeling and fear have a role," he said.
Magrath and colleagues Benjamin Pitcher and Janet Gardner studied three Australian birds: superb fairy-wrens, white-browed scrubwrens, and New Holland honeyeaters. He prompted each to sound an alarm call using a gliding model sparrowhawk. This predatory bird has a taste for fairy-wrens and scrubwrens.
The scrubwren alarm call sounds similar to that of the fairy-wren, so avian experts previously thought the birds simply thought the sounds came from one of their own.
To test this possibility, the researchers played scrubwren calls to fairy-wrens at Canberra, where these two wren populations overlap, and at Macquarie Marshes, where the two species do not live close to each other and therefore have no chance to learn each others' calls.
Sure enough, the Canberra birds did as they were "told" when played the other species' alarm calls, which was to flee pronto. The Macquarie Marsh birds did next to zilch, suggesting they hadn't learned the other species' calls.
To further test their abilities, the scientists played the alarm calls of New Holland honeyeaters to the wrens. The honeyeater vocalizations sound nothing at all like the wren calls.
Once again, the wrens demonstrated that they'd learned the meaning of other species' calls, since they fled when the honeyeater alarm sounded.
This study, published in the latest Proceedings of the Royal Society B, is unusual in that the researchers used alarm calls which, Magrath said, "are very short and everything happens quickly." These calls are intentionally brief and high-pitched, making them difficult for hawks and other predators to hear.
Other studies have found that birds also seem to understand other species' mobbing calls. He explained that these calls "are given to harass a predator not posing an immediate threat, so others can approach, look at the predator, and listen to the repeated calls of other species."
Birds seem to understand certain other birds so long as learning through association or social means is possible. They may even understand some mammals and rodents, such as small antelopes and squirrels, which appear to learn bird sounds as well.
Daniel Blumstein, associate professor and vice chair of graduate studies in the Department of Ecology and Evolutionary Biology at UCLA, told Discovery News that "this is a really timely study."
"Overall, I was not surprised by the fact that learning was important," Blumstein added, "but I liked how the study was designed so as to allow inferences about learning."
Both he and Magrath hope future studies will better determine how birds learn other calls and what motivates them to do so. It appears that one of life's most pressing emotions — fear — could be a key driving force.