A mystery that many biologists want to solve is how complexity develops in nature. And among the many social systems in the natural world, multilevel societies are distinguished by their complexity. Individuals organize themselves first into families, which are members of gangs, which are organized into clans.
At each level, the associations between components (individuals, families and clans) are structured and stable. In other words, individuals within families generally stay together, and families generally interact with other specific families in predictable ways, to form stable clans.
Such social organization has probably characterized much of human evolution (and is still common in many hunter-gatherer societies around the world).
In fact, multilevel societies have probably played a fundamental role in human history, accelerating our cultural evolution. Organizing into distinct social groups would have reduced the transmission of cultures and allowed multiple traditions to coexist.
In our research, published today in Ecology Letters, we investigated the social behaviors of a wild population of superb troglodytes. We have found that these birds also organize themselves into societies on several levels – a level of complexity once thought to be exclusive to large-brained mammals.
Breeding birds in cooperation
While we have some ideas about the benefits of corporations on many levels, we know relatively little about how and why they form in the first place.
Among the few species known to live in multilevel societies, there is one characteristic shared by all. That is, they live in stable groups, in environments where food availability is irregular and difficult to predict.
This is also true of many cooperative breeding birds, including the stunning Fairy Wren – familiar in parks and gardens in South East Australia. They breed in small family groups, with non-breeding helpers helping a dominant breeding pair. And this social system is common among Australian bird species.
The stunning Fairy Wren is a well-studied species and loved by Australians, even being crowned Bird of the Year in this year’s Guardian / BirdLife Australia poll.
These birds are known for their polyamorous approach to sex, although they are socially monogamous. Breeding pairs form exclusive social bonds, but each partner will always mate with other individuals.
Our work now reveals that this complex arrangement during the breeding season is just the tip of the iceberg.
It’s not easy to be blue – the cost of color in fairy cave dwellers
Associate by choice
We followed nearly 200 birds over two years, attaching different colored necklaces to each individual. We recorded the birds’ social associations and, from our observations, built a complex social network that allowed us to determine the strength of each relationship.
We have found that during the fall and winter months, some breeding groups (which include the breeding pair, one or more helpers, and last summer’s offspring) stably associate with others. breeding groups to form supergroups. And that was usually done with individuals with whom they were genetically related.
In turn, these supergroups associate daily with other supergroups and breeding groups, forming large communities. The following spring, these communities split into original breeding groups inhabiting well-defined territories – only to join again the following winter.
Much like humans, these little birds do not team up haphazardly during the long winter months. They have specific individuals and / or groups that they choose to be with (but we currently don’t know how they make that choice).
While it is not yet clear why the superb cave dwellers form superior social units (supergroups and communities), we believe that this could allow individuals to exploit larger areas during the winter, when food is scarce. It would also provide additional security against predators, such as hawks and kookaburras.
This theory is supported by our review of the literature, which shows that multilevel societies are probably common among other Australian cooperative breeding birds, such as noisy and bell juveniles and ridged spines.
Cooperative animal husbandry is another strategy for coping with difficult conditions such as food shortage. Thus, the conditions which favor cooperative breeding are the same as those which favor societies at several levels.
Multi-level societies in other animals
There are several other species which appear to have a similar social organization. They include primates such as baboons and other large mammals that feature rich animal cultures, such as orcas, sperm whales, and elephants.
For a long time, researchers thought that living in complex societies might be how humans developed big brains. They also believed that this characteristic may be exclusive to mammals with large brains, as it is not easy to keep track of many different social relationships (at least that is what one thought).
Consequently, other animals with which we are less close were mostly excluded from this field of investigation.
It might reflect a prejudice that we humans have towards our own species and species that resemble us.
In fact, you don’t have to be a mammal with a big brain to evolve complex societies on many levels. Even small-brained birds such as the gorgeous little Fairy Wren can do this – as well as the vulturine guinea fowl, a chicken-like bird from northeast Africa.
We strongly suspect that a number of birds will join their ranks in the years to come as more research is conducted.
Acknowledgments: We thank our colleagues Alexandra McQueen, Kaspar Delhey, Carly Cook, Sjouke Kingma and Damien Farine who are co-authors of this research.