Researchers have found that birds, like humans, form friendships with non-relatives over long periods of time.
They discovered that, while starlings preferentially helped relatives, they also frequently and consistently aided specific non-relative birds, even in situations where there were relatives available to help.
“The fact that humans who are not related by blood help each other repeatedly over time is demonstrably true — think of the ongoing mutual support that sustains your longest-running friendships,” a press release from Columbia University said. “But the idea that such interactions occur in the animal kingdom has been difficult to prove.”
The study, led by former Columbia Ph.D. student Alexis Earl, looked at more than two decades of data to show that starlings demonstrate “reciprocity” — helping one another with the presumption that the favor will at some point be returned.
“Starling societies are not just simple families, they’re much more complex, containing a mixture of related and unrelated individuals that live together, much in the way that humans do,” said Dustin Rubenstein, a professor in the Department of Ecology, Evolution and Environmental Biology, at Columbia.
Scientists have long understood that animals help out their direct blood relatives because it boosts their genetic fitness and prolongs their genes. And while starlings do give their relatives preferential treatment when it comes to giving assistance, many also help non-relative “friends.”
The researchers discovered that non-relative helping among starlings happens by forming reciprocal relationships that sometimes develop over many years.
In order to prove that this kind of reciprocal helping behavior is extended to non-relative birds, the researchers studied hundreds of African starlings living in east African savannas. For 20 years — from 2002 to 2021 — they examined thousands of interactions between birds living together in the harsh climate.
In order to pinpoint genetic relationships between individuals, the research team collected DNA samples. They discovered that while “helpers” gave preferential aid to relatives, they also often and consistently helped certain non-relative birds, even when there were relatives they could help instead.
“Many of these birds are essentially forming friendships over time,” Rubenstein explained. “Our next step is to explore how these relationships form, how long they last, why some relationships stay robust, while others fall apart.”
The data built upon decades of research already collected by Rubenstein, colleagues and students on why and in what ways animals socialize. They had previously looked at other types of animal societies throughout the world, including beetles in Asia, wasps in Africa, snapping shrimp in the Caribbean and lizards and mice in Australia.
“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 added.
The study, “Superb starlings swap helper and breeder roles with kin and non-kin,” was published in the journal Nature.
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