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.
