The surprising habits of angry fairy-wrens

Superb fairy-wrens (Malurus cyaneus) are more likely to risk life and wing to help members in their close social circle, compared to acquaintances and especially strangers, according to new research in Current Biology.

The findings indicate that, like humans fairy-wrens have a multilevel social structure and cooperate with each other in an hierarchical way.

“Both species live in multilevel societies, starting with a core group of just a few closely connected individuals,” says the person who has the wonderful task of observing the behaviour of these energetic little birds, lead author and PhD candidate at Monash University, Ettore Camerlenghi.

“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.”

Humans are more likely to share food with people from the same household, ahead of those from social units in the same community, and least with those from social units outside of their community.

Until now, scientists hadn’t tested whether these patterns of cooperation also occur in non-humans.

To do this the team studied a population of free-living superb fairy-wrens in Australia, identifying the breeding groups, the community of interacting breeding groups, and unfamiliar groups from the same population

A brown fairy wren sitting on a branch
Credit: Olivia Congdon/ANU

Co-author Professor Robert Magrath from the Australian National University told Cosmos they recorded distress calls, which are basically a cry for help when a fairy-wren is being attacked by a predator.

“Or, in our case, when you’re taking them out of mistnets and there are huge humans handling the fairy-wrens,” he says.

They then played the distress calls back to the birds, but not just in isolation; to properly simulate a predation event the researchers placed a model predator – specifically, a taxidermic laughing kookaburra (Dacelo noveaguineae) – next to the speaker.

Magrath says that even though the fairy-wrens couldn’t see the bird giving the distress call, “since kookaburras are a danger to fairy-wrens, it’s a realistic predator to have to create this illusion that something bad is happening.”

By doing this they could test how willing the birds were to help others in need.

The behaviours ranged from mobbing, where they approached and called to monitor and harass the predator to try to drive it away, to a bizarre distracting behaviour called a rodent run display.

“It’s really weird! The bird transforms itself into what looks like a mammal, so it hunches its back up, and scurries along the ground, or even on long branches, looking like a mammal rushing around,” says Magrath.

That last one is presumed to distract predators, but at great risk to the individual bird.

“We found superb fairy-wrens are careful about who they aid. They’ll risk life and limb for birds from the same breeding group, but are more careful when helping casual acquaintances,” Magrath says.

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

The results suggest that fairy-wrens can recognise the discrete social level individuals belong to and provide aid accordingly.

“Like humans, the different social levels seem to have different functions,” says Associate Professor Damien Farine, behavioural and movement ecologist and co-author from ANU and the University of Zurich in Switzerland.

“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.

“Exploring patterns of cooperation can help us understand the benefits of living in multilevel societies.”

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