At the bird feeders, there is strength in numbers

At the bird feeders, there is strength in numbers

Using data from the Cornell Lab of Ornithology, a new study finds that birds that have evolved to be more social are less likely to drive other birds away from a feeder or roost.

Spend time looking at backyard bird feeders and it becomes clear that some species are more “dominant” than others. They evict other birds from a feeder or roost, usually based on their body size. Scientists wanted to know if birds that evolved to be more social also evolved to be less aggressive.

Their conclusions published on March 1 in the Proceedings of the Royal Society B“The effect of sociality on competitive interactions among birds.”

“We found that species sociality was inversely related to dominance,” said lead author Ilias Berberi of Carleton University in Ottawa. “Using data collected from thousands of volunteer birders, we measured the sociality of different species based on their typical group size when observed at feeders. Although some species are often found in groups, others tend to be solitary. When we looked at their dominance interactions, we found that more social species are weaker competitors. Overall, the most social bird species are less likely to evict competing species from feeders.

But there is also strength in numbers in the world of birds. Despite a possibly lower level of competitiveness, social species, such as House Finch, American Goldfinch, or Pine Siskin, take the upper hand (or the wing) if members of their own species are with them. When present in groups, they are more likely to displace less social birds, such as the Northern Mockingbird or Red-bellied Woodpecker.

The study is based on 55,000 competitive interactions between 68 species common to 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 concurrently managed by Birds Canada.

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“Being a social species certainly has its advantages,” said co-author Eliot Miller, postdoctoral researcher at Cornell Lab. “Social species appear to have 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 that they tended to compete more with each other. — Pat Leonard

Pat Leonard is a writer for the Cornell Lab of Ornithology. This article was first published by the Cornell Chronicle.