Fairy-wrens calculate their benefits when coming to aid others threatened by predators

Avoiding predation is key for surviving in the wild. Credit: Dr Niki Teunissen.

A new study led by Monash University researchers, published today in Current Biology, reveals when and why purple-crowned fairy-wrens will defend others from predators.

Avoiding predation is key for surviving in the wild and helping with predator defense seems a risky, selfless act.

“Such seemingly altruistic helping behaviour has puzzled biologists for a long time, because it does not make sense to risk your own life to help others without some offsetting benefits, but these have been hard to identify,” said lead study author Dr Niki Teunissen from the Monash University School of Biological Sciences.

Dr Teunissen studied purple-crowned fairy-wrens at Australian Wildlife Conservancy’s (AWC’s) Mornington Wildlife Sanctuary in the Kimberley, Western Australia. These birds form stable social groups consisting of a dominant breeding pair and up to nine subordinates, that can help raise young and defend against predators.

“Our new approach allowed us to work out what incentives drive anti-predator behaviours in social groups,” said Dr Teunissen. She presented different types of predators, that threatened adults or the young in the nest, and measured for each helper bird whether it defended against the two types of predator.

The researchers established that subordinate fairy-wrens defend the nest more often when they are more likely to inherit a breeding position in the group in the future. The researchers could calculate exactly how likely each bird is to inherit a breeding position in the group because they have studied this species for a long time and inheritance follows strict rules.

“Our findings show that subordinate helper fairy-wrens expecting to inherit the top spot in the group invest in saving the threatened young so that they have a larger group later on when they are a breeder themselves”, Dr Teunissen said. “In other words, they are actually saving their own future helpers.”

On the other hand, when presented with a predator that poses a threat to adult group members, the subordinate fairy-wrens carefully select which group members they protect: helpers come to the aid of relatives or potential mates, both  valuable group members, but ignore threats to competitors in the group.

Professor Anne Peters, also from the Monash University School of Biological Sciences, said that these findings meant that subordinate fairy-wrens were not acting altruistically after all.

“These wrens are actually looking after their own interests, playing the long game. They are surprisingly calculated in when and who they help, making sure it benefits themselves in the long run,” Professor Peters said.

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