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Using Cornell Lab of Ornithology data, a new study finds that birds that have evolved to be more social are less likely to kick other birds off a bird feeder or a perch.

Spend any time watching backyard bird feeders and it becomes clear that some species are more "dominant" than others. They evict other birds from a feeder or perch, usually based on their body size. Scientists wanted to learn if birds that have evolved to be more social have also evolved to be less aggressive.

"We found that species' sociality was inversely related to dominance," said lead author Ilias Berberi from Carleton University in Ottawa, Canada. "Using data collected from thousands of birdwatching volunteers, we measured the sociality of different species based on their typical group size when seen at bird feeders. Though some species are often found in groups, other tend to be loners. When we examined their dominance interactions, we found that more social species are weaker competitors. Overall, the more social bird species are less likely to evict competing species from the feeders."

But there's strength in numbers in the bird world, too. Despite a possibly lower level of competitiveness, social species, such as the house finch, American goldfinch or pine siskin, gain the upper hand (or wing) if members of their own species are with them. When present in groups, they're more likely to displace less social birds, such as the Northern Mockingbird or Red-bellied Woodpecker.

The study is based upon 55,000 competitive interactions among 68 common species at backyard feeders. The data was collected through Project FeederWatch, a long-running Cornell Lab of Ornithology project that uses data collected by citizen scientists to monitor feeder birds from November through April each year. FeederWatch is also run concurrently by Birds Canada.

"Being a social species certainly has its advantages," said co-author Eliot Miller, a postdoctoral researcher at the Cornell Lab. "Social species appear to have a better defense against predators and may benefit from increased foraging efficiency."

But even though social species have fewer competitive interactions with other species, the study found they tended to compete more among themselves.

The work is published in the journal Proceedings of the Royal Society B: Biological Sciences.