These Tiny Birds Get By With A Little Help From Their Friends

Individual superb fairy-wrens help their families and friends before helping strangers, suggesting these songbirds recognize which social tier individual birds belong to

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What do people and fairy-wrens have in common? We live in groups. But what are the advantages of group living? In the case of superb fairy-wrens, there’s safety in numbers.

Well, probably.

A recent study has found that, upon hearing a distress call, superb fairy-wrens, Malurus cyaneus, are more likely to help individuals within their closest social circles than those whose calls they don’t recognize.

This complex social arrangement is known as a multilevel society. The social relationships between these groups are stable and predictable. Although multilevel societies are often structured around kinship, helping behavior itself can be independent of kinship. Even more interesting is that personal risk-taking in these tiny songbirds follows the same rules seen in groups of human hunter-gatherers.

“Both species live in multilevel societies, starting with a core group of just a few closely connected individuals”, the study’s lead author, evolutionary ecologist Ettore Camerlenghi, a PhD student at Monash University, explained in a statement. Mr Camerlenghi is especially interested in the evolution of animal societies, particularly those of songbirds, in understanding how they are organised and the roles that cooperative behavior plays within them.

But what are the benefits of multilevel societies?

We know that multilevel societies characterize and influence much of human evolution, and are typical amongst hunter-gatherer societies. Curiously, although multilevel societies are being studied in whales, elephants, and even in some primate species, this particular social hierarchy has only recently been described in birds, such as fairy-wrens.

“We found the wrens, like hunter-gatherers, have three distinct types of relations — those from the same breeding group, familiar individuals from the same community and unfamiliar birds from the wider population”, Mr Camerlenghi explained.

Superb fairy-wrens families are very tight-knit, and are comprised of two to six individuals. When not breeding, these family groups associate with other nearby families to form supergroups, and these supergroups can associate with other supergroups to form large community flocks. In the process, individual fairy-wrens develop a large number of social relationships that have varying levels of intensity.

To better understand the relationships between these tiny songbirds, Mr Camerlenghi and his collaborators trapped them and gave each bird in their wild study population a unique combination of colored leg bands. These leg bands made it possible to recognize and track all individuals using binoculars.

Whilst attaching the leg bands, Mr Camerlenghi and his collaborators recorded any distress calls that the birds produced. (Individual birds voices are, like those of people, distinct and recognizable, at least to other birds.)

When fairy-wrens hear distress calls from their family or friends, they help by using a variety of tactics, such as giving alarm calls, approaching the predator, or using a distraction tactic dubbed the ‘rodent-run.’ This particular ploy involves an individual bird closely approaching the predator, assuming a hunched posture, and scurrying to and fro like a mouse. This ‘altruistic distraction display’ confuses the predator, but it also places the individual bird that performs it at high personal risk.

To simulate a predator threatening a fellow fairy-wren, Mr Camerlenghi and his collaborators played a recording of a local fairy-wren screaming in distress next to a mounted kookaburra. Kookaburras, which are large terrestrial tree kingfishers, are voracious predators of small birds, such as fairy wrens.

Mr Camerlenghi and his collaborators tested fairy-wrens’ willingness to help others by broadcasting distress calls from an individual within the same breeding group, one from the same community, or from an unfamiliar individual outside the community, and recorded the responses of all fairy-wren-witnesses (Figure 2).

“We found superb fairy wrens are careful about who they aid”, study co-author, behavioral ecologist Robert Magrath, emeritus professor at the Australian National University (ANU), explained in a statement. “They’ll risk life and limb for birds from the same breeding group, but are more careful when helping casual acquaintances.”

What happens if an unknown fairy-wren calls for help nearby?

“As for strangers, amazingly, they completely ignored the cries for help.”

Surprisingly, this straightforward study is the first to examine the decision-making process of animals living in a multilevel society.

“Like humans, the different social levels seem to have different functions”, said study co-author, behavioral ecologist Damien Farine, an Associate Professor at ANU, an Eccellenza Professor at the University of Zurich, and an Affiliated Scientist at the Max Planck Institute of Animal Behavior. Professor Farine specializes in understanding how individuals navigate their social landscape and how social life impacts the interactions between individuals’ physiology and their environment.

In short, living in a multilevel society helps the fairy-wrens to distinguish whom to cooperate with and how much. It’s likely that cooperation at different social levels has different social functions, too.

“Core breeding units give individuals access to high value help when needed, whereas the broader society of familiar birds give wrens the power in numbers when facing predators”, Professor Farine pointed out.

Other benefits of a multilevel society at the family group level may be to increase group cohesion, survival and reproduction. At the community level, alliances between neighboring breeding groups are likely to help the birds better defend against predators, and to be less aggressive between groups.

Although humans and fairy-wrens are extremely distant evolutionary relatives (our last common ancestor lived at least 200 million years ago), it’s quite interesting that the complex pattern of cooperative behavior shown by these tiny songbirds is so familiar to us. This suggests that multilevel societies are an ancient innovation that evolved independently many times in many different species — long before humans ever appeared.

Source:

Ettore Camerlenghi, Sergio Nolazco, Damien R. Farine, Robert D. Magrath, and Anne Peters (2023). Multilevel social structure predicts individual helping responses in a songbird, Current Biology | doi:10.1016/j.cub.2023.02.050

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