The researchers think different social systems in the wild may help explain the different results. African greys live in huge, constantly shifting flocks. It might be important for the birds to immediately build good reputations, so that if they need help in the future — such as extra food, or help chasing off a predator — they’ll get it. Blue-headed macaws live in smaller, unchanging groups. So quickly building up a reputation might not be as important.

That is “a thought-provoking potential explanation,” said Katherine Cronin, an animal welfare scientist at Lincoln Park Zoo in Chicago, who has studied helpful behavior in animals.

Scientists call this kind of helpful behavior prosocial. Dr. Cronin said earlier research might lead to the opposite prediction: that the small-group-living macaws would behave more helpfully, while the African greys might not need to. She also wondered whether the blue-headed macaws just didn’t understand their partners’ needs.

However, Dr. Cronin added, scientists who study such behavior in animals have often come across results that challenge their existing ideas. Finding and testing new hypotheses will help us understand why some animals have evolved to lend a hand.

“In humans, it’s known that we help others because we empathize with them,” Dr. Brucks said. But researchers can’t tell whether African grey parrots feel the same way, or help others simply because they expect favors in return.

They also don’t know how common it is across the animal kingdom for individuals to help each other out. Dolphins, rats and vampire bats have been all observed giving help. Dr. Brucks says only a few apes, though, have acted like the African grey parrots, aiding others with no clear benefit to themselves.

What is clear is that humans aren’t the only species that helps each other, Dr. Brucks said. Over hundreds of millions of years of evolving separately, we and the African grey parrots both developed the habit of looking out for a neighbor who needs a walnut.