Iconic Australian fairy-wrens live in complex multilevel society, international study finds
A new study led by Monash University ornithologists has found that the diminutive superb fairy wren likes to organise itself into a complex multilayered society – a social feature once believed to be exclusive to big-brained mammals such as humans, primates, whales and elephants.
The discovery is published today in Ecology Letters.
Although scientists have ideas about the advantages of multi-level societies, they know relatively little about how and why multilevel societies form in the first place.
“One characteristic the few species known to live in multilevel societies share is that they live in stable groups, in environments where food availability is inconsistent and difficult to predict,” said lead study author Ettore Camerlenghi, a PhD candidate at the Monash University School of Biological Sciences.
The research team studied social behaviour in a wild population of superb fairy-wrens, that breed cooperatively in small groups. They tracked almost 200 birds over two years by attaching a different coloured leg band to each individual. During this time, they observed who was hanging out with who and used their observations to build a complex network of the birds’ social associations.
“Superb fairy-wrens were already notorious for their polyamorous approach to sex, which surprised the world as the breeding groups are strictly territorial, and the breeding pairs form exclusive, seemingly monogamous, social bonds,” Ettore said.
Study co-author Professor Anne Peters said the research revealed the birds’ social behaviour during the breeding season was just the tip of the iceberg of a highly complex social life year-round.
“In superb fairy-wrens, three distinct, stable, hierarchical social units emerge over the year to form a multilevel society,” Professor Peters said.
“During the breeding season superb fairy-wrens live in exclusive territorial breeding groups - however, the boundaries between groups (and their territories) collapse after the breeding season.”
The researchers found that during the Autumn and Winter months, some breeding groups stably associated with other breeding groups, to form supergroups. And these in turn associated with other supergroups and breeding groups on a daily basis, forming large communities.
During the following Spring, these communities split back into the original breeding groups inhabiting their well-defined territories – only to join again in the next winter.
“We discovered that, just like humans, these little birds don’t associate with each other at random during the long Winter months,” said Ettore.
“Instead, they have specific individuals or groups they prefer to spend time with.”
Professor Peters said at this stage it was not known why some groups associated with specific other groups – perhaps to seek safety against predators, or to find future sexual partners.
“Our research, through a literature study, also shows that multilevel societies are likely to be quite common among other cooperatively breeding birds, of which Australia has many, such as the familiar noisy and bell miners and some thornbills,” Professor Peters said.
There is now good evidence that you don’t need to be a mammal with a big brain to evolve complex multilayered societies.
“We now know that small-brained birds such as the superb fairy-wren live in multilevel societies, and we strongly suspect quite a few Australian birds will join their ranks over the next years,” said Ettore.