We usually associate friendship with human behavior, considering our exclusive domain. And that’s a fair assumption, as we don't often find animals boasting cooperative relationships beyond their blood relatives. The only complex "friend-like" relationship seen in vertebrates is known as cooperative breeding, in which two individuals assist in raising the young. Yet, for African starlings, the bonds they form go far beyond mere parenting duties.
We know animals form helping relationships with direct blood relatives. However, the occurrence of long-running friendships among non-related animals has long been debated. Proving such social behaviors is extraordinarily difficult without a large amount of data.
Now, a new study with 20-years of field data, published in the journal Nature, has discovered that the African superb starling (Lamprotornis superbus) forms mixed-kin groups with anywhere from 7 to 60 members, living similarly to how we humans do.
“Starling societies are not just simple families, they’re much more complex, containing a mixture of related and unrelated individuals that live together,” explains Professor Dustin Rubenstein of Columbia University.
African superb starlings belong to the starling family, living over 15 years and growing up to 19 cm in height. The study analyzed starlings from central Kenya that breed twice a year, during rainy seasons. After surveying for over 40 consecutive breeding seasons, researchers were able to decipher the relationship between breeders and helpers.
They found each breeding pair was aided by up to 16 non-breeders, i.e., helpers. This aid even included foraging for the hatchlings and defending the nest from predators. In return, this helped in group augmentation, increasing group size. The adult survival rate of larger starling groups was seen to be higher than that in smaller groups.
Apart from the benefits of group augmentation, the study also suggests that within-group reciprocity may proliferate complex cooperative societies.
However, this doesn’t mean that the helpers are unbiased with blood relatives and non blood relatives. Starling helpers still preferred kin, but also actively and consistently assisted unrelated individuals. Researchers hypothesize kin discrimination might be the outcome of past work among starlings that favored close relatives first.
Robert Trivers' seminal 1971 paper on reciprocal altruism in the animal kingdom – a much-studied theory in evolutionary biology – identiified that these kinds of cooperative behaviors among animals were likely widespread, as individuals invested short-term energy in another, trusting that there'd be some benefit in the future. Since then, scientists have been eager to prove this beyond hypothesis. But we still don't know a lot about what drives it – except that many animal social structures are more complex than early research suggested.
“Many of these birds are essentially forming friendships over time," Rubenstein said. "I think this kind of reciprocal helping behavior is likely going on in a lot of animal societies, and people just haven’t studied them long enough to be able to detect it."
The study was published in Nature.
Source: Columbia News
