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Imagine a world where animals, like humans, form friendships that endure for years. A world where alliances are forged not through blood ties but through acts of mutual aid. This world exists in the African savannah, where birds like the African starlings engage in reciprocal helping behavior, a concept once thought exclusive to humans.

A new study led by Alexis Earl, a former PhD student at Columbia University in Professor Dustin Rubenstein’s lab, has cracked open the complex social world of these birds. The findings challenge long-held assumptions that kinship alone drives cooperative behavior.

Instead, the study reveals that starlings form lasting friendships, built on the expectation that help given today will be returned tomorrow.

African starlings: More than family groups

African starling societies are anything but simple. These aren’t just tight-knit family groups. They’re intricate networks of related and unrelated individuals, living together, helping each other, and occasionally switching roles.

“Starling societies are not just simple families,” Rubenstein said. “They’re much more complex, containing a mixture of related and unrelated individuals that live together, much in the way that humans do.”

The research team observed these birds over 20 years at the Mpala Research Centre in Kenya. During 40 breeding seasons, they documented thousands of interactions among hundreds of birds. By collecting genetic data, they could trace familial ties and map out the social networks within each group.

Birds help non-relatives

The data revealed a striking pattern. Birds weren’t just helping relatives, they were helping non-relatives too.

And not just once – over and over again. These birds were forming relationships based on reciprocity, where the expectation wasn’t immediate repayment but long-term support.

Rubenstein emphasized the significance of these findings. “Many of these birds are essentially forming friendships over time,” he said.

But why help a non-relative when a relative is nearby? For the starlings, the answer appears to lie in building a network of allies, a safety net that extends beyond family bonds.

Role reversals and unexpected alliances

Starlings don’t stick to one role. They don’t remain helpers or breeders for life. Instead, they switch roles throughout their lifetimes, a phenomenon rarely seen in cooperative breeders.

The researchers found that individuals frequently moved between helper and breeder roles, sometimes even after raising their own offspring.

This role-switching opened the door for reciprocal helping. A bird that helped another during one breeding season might later become a breeder and receive help from that same individual.

The study tracked 528 helper-breeder pairs, and in 142 pairs, the same two birds swapped roles and helped each other over time.

Bird friendships form through reciprocal helping

Kin selection is a well-established concept in evolutionary biology. Helping family members ensures the survival of shared genes. But the researchers observed a different kind of bond in starlings – one based on reciprocity, not kinship.

Resident males typically helped relatives. Immigrant males, however, helped both kin and non-kin. In fact, the researchers found that the helping rate for reciprocating pairs was 242 percent higher than for non-reciprocating pairs.

Clearly, these birds were forming alliances that went beyond genetic ties.

But kinship wasn’t entirely irrelevant. Resident females rarely became breeders, so they had fewer opportunities for reciprocal helping. Immigrant females, on the other hand, often moved between helper and breeder roles, forming bonds with specific non-relatives.

Power of long-term data

The depth of this study lies in its duration. Twenty years of observations, over 12,000 recorded helping interactions and more than 500 individual birds.

This long-term dataset allowed the researchers to detect subtle patterns that would have been invisible in a shorter study.

Rubenstein believes these findings have broader implications. “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,” he said.

Without such extensive data, the role of reciprocal helping might have remained hidden beneath the more obvious kin-based helping patterns. The study underscores the importance of sustained observation in uncovering the intricacies of animal behavior.

Implications for animal social networks

Why would a bird help a non-relative, even when a relative is nearby? The answer may lie in the unpredictability of life in the African savannah. Food scarcity. Predator threats. Uncertain breeding success.

In such an environment, forming bonds with non-relatives could serve as a form of insurance. Birds that help today may receive help tomorrow when conditions worsen. It’s a strategy that maximizes survival, not just for the individual but for the entire group.

The researchers observed that these reciprocal bonds sometimes lasted for years. And in some cases, they were even stronger than bonds formed through kinship.

By maintaining these alliances, birds could increase their chances of receiving support during critical breeding periods.

Reciprocal helping in other birds

This phenomenon isn’t limited to African starlings. Other bird species, such as green woodhoopoes and white-fronted bee-eaters, also exhibit reciprocal helping. However, the evidence of such behavior in non-relatives is rare.

The researchers argue that reciprocal helping may be more common than previously thought. The problem is that detecting it requires long-term observation – years, even decades. And that kind of data is difficult to obtain.

In the case of African starlings, the data revealed that reciprocal helping relationships sometimes persisted for multiple breeding seasons. Birds that helped each other one year often maintained that relationship, swapping roles and continuing to support one another over time.

Future research directions

What drives birds to choose specific partners for reciprocal helping? How do they recognize reliable allies? Are there cues – vocal signals, visual displays, prior interactions – that indicate trustworthiness?

The study raises more questions than it answers. The researchers plan to expand their observations to other species within the same environment. By doing so, they hope to determine whether reciprocal helping is a widespread strategy among cooperative breeders or a unique trait of African starlings.

Additionally, they aim to explore the impact of environmental factors on reciprocal helping. Does food scarcity strengthen these bonds? Do predator threats prompt birds to seek new allies?

Redefining animal cooperation

The findings of this study challenge the conventional view that cooperative behavior in animals is driven solely by kin selection. While helping relatives remains a vital strategy, reciprocal helping may play an equally significant role in stabilizing social groups.

For the African starlings, reciprocal helping is a way to build alliances, secure support, and hedge against future uncertainties. It’s a strategy that mirrors human friendships – complex, enduring, and sometimes unpredictable.

“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,” Rubenstein said.

The study, published in Nature, provides a rare glimpse into the hidden world of animal friendships. It shows that even in the harsh and unpredictable environment of the African savannah, social bonds can form, endure, and evolve.

And in the end, the birds that help today may just be the ones receiving help tomorrow.

The study is published in the journal Nature.

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