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Feeders might seem like friendly spots where chickadees, finches, woodpeckers, and nuthatches can kumbaya over a good meal, but that couldn't be further from the truth. Some of the most intense avian rivalries are hashed out among the seeds and suet, says Eliot Miller, a researcher at the Cornell Lab of Ornithology and author of . “Feeders are these arenas where birds gather and fight," he says. "There’s an increased rate of aggression to some degree.”

By combing through thousands of observations from , a volunteer science count that runs from November to April, Miller involving 136 common North American species. As birds compete for access to feeder supplies, they reveal where they belong in the pecking order. So, by simply noting which species flew off and which ones stood their ground, Miller and his colleagues were able to build a database of victors and losers. They then used some complex statistical modeling to sort those interactions into clear levels of domination. In general, they found that bigger birds were more intimidating. A chickadee may be spunky for its size, but at half an ounce, it stands little chance against a four-pound Common Raven.

Some of the winners were a little more surprising. For instance, Downy Woodpeckers were feared despite their small stature. Miller is convinced it’s because of their formidable bills, which are used for hammering into trees and could double as battle gear.

Hummingbirds also defied their delicate reputations and came out on top. “They need to feed really regularly. In short, they don't really want to take any crap from anyone else,” Miller says. “I think that has played out over an evolutionary time scale where things like hummingbirds are very quick to be aggressive.” Their moxie allows them to push warblers and wrens away from nectar feeders.

The best part is that Miller’s study is far from over. “The database has doubled in size since I wrote the paper,” he says. “I’m constantly shocked by what people see.” He recently received an email about a grackle catching and eating chickadees that stood in its way (morbid, but not shocking). As more observations roll in, he’ll use them to look at how standings differ in various parts of the country. For now, though, he’s amazed by how well the patterns have held.

You can test Miller’s matchups by paying close attention to your own feeders during . Here are five duels to look out for, as well as some important stats and facts for each species. Just hover over or tap the images to find out more about the contenders.  

American Goldfinch vs. Black-capped Chickadee

Photos from left: Michele Black/Great Backyard Bird Count; John Pizniur/Great Backyard Bird Count

Both of these birds are low on the feeder totem pole, but goldfinches have a slight edge in size. Still, Black-capped Chickadees are far more aggressive than American Goldfinches, meaning that they tend to get the prime spot.

Winner: Black-capped Chickadee

Mourning Dove vs. House Sparrow

Photos from left: Michele Black/Great Backyard Bird Count; Melanie Neault/Great Backyard Bird Count

Mourning Doves are known for their passive natures, so their overall dominance score is far weaker than their bulk suggests. Yet they can beat out House Sparrows, which weigh about as much as a slice of bread (though they’re a lot more aerodynamic).

Winner: Mourning Dove

European Starling vs. Blue Jay

Photos from left: Jean Turgeon/Great Backyard Bird Count; Daniel Irons/Great Backyard Bird Count

These two species are perfectly matched, despite the Blue Jay’s heavier weight and bullying nature. Miller has noticed that introduced species like starlings often don’t fit neatly into the predicted pattern; he thinks this might have to do with how successful they've been at thriving in new environments.

Winner: Draw

Common Raven vs. American Crow 

Photos from left: Deidre Lantz/Լ����Ƶ Photography Awards; Brian Kushner

Ravens are much heavier than crows and can beat them in any one-on-one battle. But when there's a groups of crows, the story is quite different. While ravens are typically solitary birds, crows work together to push rival species out of their territory.

Winner: A murder of American Crows

Pileated Woodpecker vs. Red-bellied Woodpecker

Photos from left: Bruce Harris/Great Backyard Bird Count; Matthew Pimm/Լ����Ƶ Photography Awards

You might think all woodpeckers are created equal. Not so. Miller’s research found that there are obvious hierarchies within genuses, as seen with Red-bellieds, which dominate the feeder scene when compared to their larger Pileated cousins. Miller says we need more science on why, but in the meantime, just put your money on the Red-bellied’s classy coat.

Winner: Red-bellied Woodpecker