Local birds are expert eavesdroppers

Most humans are well versed in the art of eavesdropping. We learn it at an early age by listening in to hushed conversations between our parents or older siblings.

It turns out we aren’t the only ones who like to eavesdrop – it’s common in animals around the world. But such eavesdropping is much more than just a simple case of curiosity, it helps animals glean useful information about the world around them.

One important reason for eavesdropping is to find out about danger. Most animals are vulnerable to predators, and many birds and mammals have alarm calls that warn others of the same species about danger. But as well as paying attention to alarm calls of their own species, it pays to eavesdrop on the alarms of others.

Eavesdropping on other species helps keep animals out of danger, by creating a kind of ‘neighbourhood watch’ on the lookout for predators.

But this eavesdropping on other species’ calls creates a puzzle. How do birds recognise these ‘foreign languages’? For a long time it was suspected that birds innately understood what other species were saying, perhaps because alarm calls are often loud or harsh.

Now it’s been discovered birds can quickly learn to recognise different alarm calls.

Professor Robert Magrath has been studying birds in the National Botanic Gardens in Canberra for more than 25 years and says they’re much smarter than we might think.

“‘Bird brain’ is actually a compliment,” he says. “Birds can learn all sorts of useful things to help them negotiate the challenges of life.”

He and his colleagues found local species can learn to eavesdrop on each other’s calls. Fairy-wrens on the campus of ANU, for example, recognise noisy myna alarm calls. The noisy mynas are another common campus bird, so there’s plenty of opportunity for wrens to learn what they mean. Across the road in the Botanic Gardens, where mynas are absent, the wrens don’t understand their calls.

Magrath’s latest study, which involved researchers from ANU and the University of Bristol in the UK, found fairy-wrens can learn that a new call means ‘danger’ without even having to see a predator.

Team members played back novel sounds, which were originally ignored by the wrens, at the same time as a chorus of familiar alarm calls from local common species.

They found after just two days of training, most of the wrens fled to cover after hearing the new sound – they’d learnt it was an alarm call. This is a form of social learning (learning from others) rather than learning from direct experience with the predator. Magrath points out this can be particularly useful in situations where learning by direct experience could prove fatal.

Learning by listening will also help birds in dense habitats, when it can be difficult to see a predator or bird sending alarm calls.

The group is already looking into how their findings could help protect some of our endangered species.

“The beauty of learning is that it helps animals change their behaviour according to their environment,” Magrath says.

“When threatened species are released into the wild after captive breeding, they are often not very good at avoiding predators. Our work suggests we could potentially teach them to recognise alarm calls from the release site. Captive breeding programs are expensive, so any extra chance for survival is worth investigating.”

This work on eavesdropping serves as a kind of wake-up call, highlighting that human interference can have ripple effects on natural communities.

“If you drive a species to extinction, it means not only is that species missing from the community, but any information it provided about danger is also missing,” Magrath says.

“In the Botanic Gardens, for example, New Holland honeyeaters are very observant and have very loud alarm calls, so they’re an important source of information about hawks for other birds. If you took away that species you’d put others in greater danger.”

The team is now trying to work out how birds use all this information about danger without finding themselves constantly ducking for cover.

“Other species can be vulnerable to different predators, so their calls won’t always be relevant, and there’s always the problem of false alarms,” Magrath says.

“Birds will therefore have to balance their own knowledge of the world with the information gained from eavesdropping on others.”