These birds establish bonds of friendship to help each other raise their chicks.

There are years when barely a few chicks survive, even though they breed twice a year. In the African savannah, conditions are so harsh for superb starlings ( Lamprotornis superbus ) that if it weren't for their cooperative breeding, they would probably have become extinct long ago. Now, a study based on 20 years of observations and published in Nature has discovered that each season, a few breed and many provide care, without any kinship ties between them. In fact, most of the help is provided by immigrants. In return, those who act as helpers at one season will receive assistance from the same people they assisted when it is their turn to breed later on. This reciprocity between unrelated individuals is an extremely rare animal behavior .

Although there are patches of dry forest in the nearly 20,000 hectares of the Mpala Research Centre (Kenya), the savannah rules. The superb starlings nest in the thorny bushes of this park, but they must contend with a myriad of predators, which reach their nests both on the ground and in the air. This area of ​​East Africa has two rainy seasons: the short one (October to January) and the long one (March to June), which these colorful birds take advantage of for double laying. But the weather is very erratic, and there are years when the weather skips one of the seasons. These are the conditions in which these starlings breed. They do so cooperatively: some pairs reproduce while the others help raise the chicks. It is estimated that 10% of bird species exhibit this behavior .

“Rainfall (and therefore food availability) is very unpredictable from year to year. This makes conditions very harsh and uncertain for birds,” says Dustin Rubenstein, ornithologist at Columbia University (USA). At the turn of the century, Rubenstein first visited Mpala as part of his doctorate. “We’ve been doing fieldwork continuously since 2001, 25 years ago. I go once a year, but I’ve been spending less and less time there lately,” he says. Now, students in his lab spend hours observing flocks of superb starlings. The results of two decades of observations and 40 breeding seasons have revealed just how special these four-colored birds are.

In the nine flocks they study, each with dozens of members, they have found that only a small proportion of them breed, an average of about seven pairs. The remaining individuals, up to 17 per pair, act as helpers, providing food for the chicks or defending the nest. Giving up on procreating, on having offspring, is evolutionarily absurd, unless those raising them are your relatives; only then do your genes ensure continuity; this is what is called kin selection.

Rubenstein's team, which had ringed 1,175 superb starlings to identify them, had also taken genetic samples to determine their degree of relationship. This led them to confirm that these birds do indeed help their relatives raise their young. But what they also discovered was that in many cases, there was no relationship between the helper and the breeding pair.

In fact, both females and males from other groups played a leading role in helping others. If forgoing procreation in favor of a relative might be senseless, doing so in favor of strangers is the closest thing to ecological suicide. But it turns out that the role of immigrants is vital. “Because they live in hostile and unpredictable environments, reproduction is low and irregular over the years,” Rubenstein explains. “Groups cannot subsist solely on producing offspring. They need to allow the incorporation of unrelated immigrants of both sexes. Without them, the groups would disintegrate and become extinct, becoming too small to persist,” he adds. However, to recruit helpers from outside, they must allow them to reproduce. And this is what they have also found. After a few seasons of breeding as helpers, a role reversal occurs, and the immigrant can procreate while being helped by the residents. Up to 73% of the individuals switched roles for more than one season.

But help is neither arbitrary nor random. Those who breed one season and change helpers the next tend to assist the same people who helped them in the past, in a very rare case of mutual assistance. “These relationships of reciprocal help serve to stabilize these mixed-kinship societies, which must form in these harsh and unpredictable environments if the groups are to avoid extinction,” Rubenstein explains. Help, especially from outsiders, has another positive effect: as they demonstrated in another study , as group size increases, the chances of survival (including their own) increase.

Altruism without sexual interest

When we delve deeper into reciprocity, the picture becomes more complicated. Direct and immediate interest—for example, helping a potential future partner—doesn't seem to count here. Half of the mutual-aid relationships were between members of the same sex. Altruism—helping without expecting anything in return or with an obvious benefit—is exceptional and reserved for a few species, such as great apes and some other mammals . Rational calculation and future expectations are at work among humans, but it seems a bit of a stretch to imagine such cognitive abilities in these birds. "Many of these birds are forging friendships over time," Rubenstein says. "Our next step is to explore how these relationships form, how long they last, and why some remain strong while others fall apart," he concludes.

Biologist Irene García Ruiz , who worked in Rubenstein's lab, points out that cooperative breeding has many forms along a continuum ranging from eusocial insects, such as ants or bees, among which only one, the queen, procreates, to isolated pairs. In between are starlings, but also humans, especially those in traditional communities . "What's a bit difficult to explain is why you're going to invest time and resources in raising other individuals that aren't your offspring," says this researcher, who is not involved in the study of superb starlings. "Almost all the literature on this topic is based on kin selection. And what we're discovering, increasingly, is that it's not the only reason they help each other, although it does play a key role," she adds.

Twenty-two years ago, Spanish researchers discovered that the Iberian starling , a bird that also practices cooperative breeding, already had this role exchange between helper and breeder. “Among birds that breed cooperatively, being a helper is the first step toward being a breeder. They help while waiting for their turn, but once they are breeders, they no longer help,” says biologist and professor at the University of Malaga, Juliana Valencia, first author of that 2003 study. “In these starlings, as in the Iberian starling, there is a role exchange,” notes Valencia, who spent more than two decades studying these birds. “At the end of June, the end of the breeding season and when the heat was at its peak in the fields of Badajoz where we studied them, we observed how the number of helpers in the last nests reached 11 or 12, while at the beginning of the season it was two, one, or none,” she adds. It's as if they were lending a hand in the most critical moments. Valencia is convinced that among the Iberian wagtails, in addition to role exchange, there was also reciprocity and mutual aid, like among starlings. "I have the data, but I've never published it," she adds.

Valencia acknowledges that ecologists and ethologists don't like the idea of ​​reciprocity without kinship. First, because it's difficult to demonstrate. "It can only be done with long-term studies, and who's going to fund you to research the same thing for 20 years?" he laments. Second, because recognizing that animals can exhibit behaviors very similar to altruism presupposes cognitive abilities that not everyone accepts. "The problem is that we want to humanize all animal behavior, and many behaviors have evolved without human intervention," he concludes.