Eavesdropping Birds Learn

The superb fairy-wren is a pint-sized bird endemic to south-eastern Australia. The male of his species boasts an iridescent blue plumage, while the female is a less impressive — but still adorable — dusty grey-brown.

These creatures are impressive for many reasons; once such reason is that they are social learners, just like humans. A study published earlier this year found that superb fairy-wrens listen in on the conversations of other bird species and can learn to react to their alarm calls warning them of predators.

This ‘eavesdropping’ method of social learning has been demonstrated for the first time in fairy-wrens by a group of biologists from the Australian National University (ANU).

The team was led by Professor Robert Magrath from the ANU Research School of Biology who has been studying the behaviour for this commonly found avian species for several years. The experiments were conducted in the National Botanical Gardens of Canberra, home to a vast variety of wild birds, including hawks which are natural predators of the fairy-wren.

Listen and learn

The researchers simulated a cacophony of sounds made by birds in the wren’s natural habitat. The wrens heard alarms calls of birds belonging to the same species (conspecific alarm calls) and alarms calls of animals belonging to other species (heterospecific alarm calls). Within these various alarm calls drawn from sounds of local species was buried a sound new and unfamiliar to the wrens. The team used stereo speakers placed at a distance of 3-6 m apart to deliver this mix of calls which differed during each playback.

The amalgamation of sounds did not confuse the fairy-wrens who were able to make the distinction between the calls of their friends and potential foes. This acoustic ‘plucking out’ of unfamiliar sounds embedded within the chorus of familiar sounds occurred rapidly, after just two days of training and even though there was no predator in sight, the birds learned to flee to safety. Moreover, the effects of this learning persisted over the entirety of the period that the birds were observed for which was one week.

Not just being cagy

To ensure that the wrens were not just being overly cautious, the researchers used a synthesised ‘control sound’ produced using a computer program. The wrens did not respond to this in the same manner as they responded to the test sounds showing that they did indeed learn to respond to the unfamiliar sound as if it were a real alarm call prompted by the presence of a predator.

Learning through exposure

Previous studies have shown that animals can learn to flee from unfamiliar sounds if they can associate those with life-like models of predators. This is a form of asocial learning.

In fact, previous experiments conducted by Professor Magrath’s team showed that after just two days of training, fairy-wrens learned to flee from unfamiliar sounds when these were coupled with life-size model gliders of known predators flying overhead (sparrowhawks or currawongs). They did not flee when they heard the unfamiliar sounds in insolation without the visual cues of the model gliders.

However, according to the researchers, learning about predators by being directly exposed to them could be fatal. Also, learning to react to hunters through visual cues is not always possible as predators are often hard to spot in the natural habitat. Fairy-wrens may find them hard to spot from high up in trees, predators tend to move fast through thick foliage, or they may even be unfamiliar to the wrens.

On the other hand, learning to associate novel sounds with those of known alarm calls, through what the authors of the current study dub acoustic-acoustic association, is a form of social learning. This can provide animals with vital information necessary for survival.

Social learning helps animals survive and thrive

This form of cooperative communication and learning strategy can be ecologically important. The authors postulate that social learning is important because it can lead to rapid spread of behaviour through a
population. The fairy-wrens can learn that a new sound means ‘predator’ without having to see a predator or even see callers fleeing for cover.

In fact, the results of this study help explain why eavesdropping is so common across other species too.

Listening in and learning could also help teach the young among the species to learn to stay away from harm.

Importantly, this research has implications for teaching animals that have been raised in captivity as part of breeding programs to help them recognise the alarm calls of predatory species and flee to safety. Teaching them these important skills at the release site could help them survive once they have been returned to the wild. Given how expensive captive breeding programs can be, research like this could be applied to help bolster the chances of survival of some of our most endangered species.


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