True friends, most people would agree, are there for each other. Sometimes that means offering emotional support. Sometimes it means helping each other move. And if you’re a superb starling — a flamboyant, chattering songbird native to the African savanna — it means stuffing bugs down the throats of your friends’ offspring, secure in the expectation that they’ll eventually do the same for yours.
Scientists have long known that social animals usually put blood relatives first. But for a study published Wednesday in the journal Nature, researchers crunched two decades of field data to show that unrelated members of a superb starling flock often help each other raise chicks, trading assistance to one another over years in a behavior that was not previously known.
“We think that these reciprocal helping relationships are a way to build ties,” said Dustin Rubenstein, a professor of ecology at Columbia University and an author of the paper.
Superb starlings are distinctive among animals that breed cooperatively, said Alexis Earl, a biologist at Cornell University and an author of the paper. Their flocks mix family groups with immigrants from other groups. New parents rely on up to 16 helpers, which bring chicks extra food and help run off predators.
Dr. Rubenstein’s lab has maintained a 20-year field study of the species that included 40 breeding seasons. It has recorded thousands of interactions between hundreds of the chattering birds and collected DNA to examine their genetic relationships. When Dr. Earl, then a graduate student in the lab, began crunching the data, she and her colleagues weren’t shocked to see that birds largely helped relatives, the way an aunt or uncle may swoop in to babysit and give parents a break.
But to their surprise, they found that starlings also helped nonrelatives, including when they might have helped family instead. Birds new to the flock helped those born within it, and vice versa. And because superb starlings often switch between breeding and helping roles, the team found that individual birds that helped nonrelatives one breeding season later had their good deeds repaid, sometimes repeatedly.
“The starlings are consistently investing in the same preferred social partners over their lives,” Dr. Earl said. “To me, that sounds like friendship.”
The idea that animals might establish friendships with unrelated individuals has provoked controversy among scientists, said Gerald Carter, an animal behaviorist at Princeton University and an author on the paper. However, a growing body of research has led scientists to accept that long-term reciprocal relationships exist among primates, elephants, crows and whales. There are also vampire bats that share blood meals with unrelated, hungry colony members, and unrelated, male Lance-tailed manakins serve as “wingmen” for each other to gain female attention.
But long-term relationships can be difficult to detect, Dr. Rubenstein said. The team needed 27 seasons’ worth of data to pick up hints of reciprocity in the starlings. He thinks they’re still underestimating it.
Such reciprocal helping relationships are probably more important than the lab’s data shows, Dr. Rubenstein said. “And so only with a lot of long-term data can you get at that.”
The study makes a convincing case, said Jorg Massen, a behavioral ecologist at Utrecht University in the Netherlands who was not involved in the paper. One next step would be to work out how these long-term relationships are maintained day to day.
“Is it just based on the reproductive help, or is it accompanied by other behavioral traits?” he said.
The behavior of superb starlings also suggests that sustaining these sorts of relationships with unrelated fellows benefits everybody. “Birds that live in larger groups tend to live longer, and they tend to reproduce more offspring over their lifetime,” Dr. Rubenstein said. In the harsh and unpredictable African savanna, it’s all hands on deck to raise young. And the addition of immigrant birds is required to make the groups more resilient.
It has parallels with the evolutionary trajectory of humans — a lineage of sociable, cooperatively breeding apes also forged on the savanna, Dr. Rubenstein said.
And today, as many experts worry about an epidemic of human loneliness, there could be value in heeding lessons from the superb starling. In other words, strong relationships are often built from providing help.
But maybe don’t offer to stuff bugs down the mouths of your friends’ kids. Luckily, you can always offer to babysit.
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