(CNN) Only a few mammals -- humans and a few other primates -- are thought to spontaneously help one another.
Now, however, scientists say African grey parrots voluntarily help each other to obtain a reward of nuts. They say it's the first time such behavior has been seen outside of mammals.
"We found that African grey parrots voluntarily and spontaneously help familiar parrots to achieve a goal, without obvious immediate benefit to themselves," said study co-author Désirée Brucks, a researcher at the Max Planck Institute for Ornithology in Germany.
The researchers studied two types of parrot -- the African grey and the Blue-headed macaw. Both species were eager to trade a metal token with a researcher in exchange for a nut treat. However, only the African grey parrots were willing to transfer a token to a neighboring parrot, allowing the fellow bird to earn a nut reward.
"Remarkably, African grey parrots were intrinsically motivated to help others, even if the other individual was not their friend. So they behaved very 'prosocially,'" said study co-author Auguste von Bayern, also a researcher at the Max Planck Institute.
"It surprised us that seven out of eight African grey parrots provided their partner with tokens spontaneously -- in their very first trial -- without having experienced the social setting of this task before and without knowing that they would be tested in the other role later on. Therefore, the parrots provided help without gaining any immediate benefits and seemingly without expecting reciprocation in return."
The reason for the helping behavior isn't clear, but the parrots appeared to understand when their help was needed. If they saw the other parrot had an opportunity to receive a nut, they'd pass a token over. Otherwise, they wouldn't bother. It didn't matter if the parrot was their friend or not, although when the parrot in need of help was more familiar the helper transferred more tokens.
"I think we can't make any clear conclusions about why. It's a pilot study showing they can help. Are they showing empathy, or another underlying mechanism [like] reacting to simple cues?"
But, Brucks continued, "what surprised me in the African greys was that they readily transferred tokens to make sure their partners got the reward. They didn't stop. They really wanted to make sure the partner got the food on the very, very first go -- when they didn't know the roles would be reversed. There was an intrinsic desire to help."
The researchers called the behavior "proactive instrumental helping" -- something that has previously only been reported in similar experiments with orangutans and bonobos.
This kind of helpful behavior isn't seen in gorillas, chimpanzees or, for that matter, crows -- another bird known for its big brain size relative to its body and problem-solving behavior, the researchers said. They added that more research was needed to see how widespread this helping behavior was among the 393 different parrot species.
Brucks said there are interactions in nature where favors appear to be given and paid back -- such as birds collectively mobbing away predators -- but it was only under controlled conditions that researchers could really get a good look at what's going on.
The findings are the latest in a string of studies that suggest some birds are much smarter than their small brains may indicate.
Puffins have been observed using tools, and vulturine guinea fowls in Kenya have been found to display complex social behavior more typically found in mammals.
"I think we have underestimated birds," said Brucks. "They haven't been the focus of cognitive studies; we've been too focused on our close relations like primates."