Their work illuminates an elaborate hidden hierarchy: Northern mockingbirds and red-bellied woodpeckers are pugnacious for their size, but both would give way if a truly dominant bird like an American crow descended upon the feeder. Tiny hummingbirds can’t afford to lose precious seconds of feeding time and thus punch way above their weight, while the pileated woodpecker, whose fearsome bill and impressive build gives it the aspect of a holdover pterodactyl, actually proves docile for its size.
Among the most common feeder visitors, the American crow is king, while tiny chickadees get pushed around by just about everybody. The oblivious mourning dove outweighs many rivals but proves relatively peaceful. And lively goldfinches love to squabble but are limited by their half-ounce size.
“You see it at your feeder, and you’re like, ‘Oh, that woodpecker? He’s a mean one!’ and you ascribe these individual preferences to birds at your feeder,” said Cornell University ornithologist Eliot Miller. “But if you zoom out, all these same interactions are happening millions of times in cities across the continent, and the way they play out is predictable.”
Every year since 1987, thousands of backyard birders from around the U.S. and Canada have reported the species they saw at their feeders during the winter as part of Project FeederWatch, a long-running data set from the Cornell Lab of Ornithology and Birds Canada beloved by ornithologists. Since 2016, participants have also been able to report interactions, such as when one bird swoops in and chases another from a prime spot on the seed feeder.
Project FeederWatch leader Emma Greig, a Cornell ornithologist, said this competition for food makes FeederWatch uniquely suited to behavioral studies.
“The birds are at a food source, so it’s a place where they’re more concentrated and even more likely than usual to have these behavioral interactions,” Greig said, noting the project’s network of 30,000 citizen-scientists meant they could collect that data at a continental scale.
In a 2017 study in Behavioral Ecology, Miller, Greig and their collaborators fed the first wave of that data into algorithms to condense a web of relationships into a simple rank. That rank not only reflects the relationship of frequent combatant pairs such as the house sparrow and the blue jay, but also accurately predicts which bird will dominate when two distant species meet for the first time.
Now Miller has provided The Washington Post with a vastly expanded data set from Greig’s citizen-scientists — 99,376 interactions between almost 200 species, up from 7,685 interactions in the 2017 study — and shared the methods needed to produce the most detailed bird power ranking yet published. Predators aren’t included as their relationship with these birds is not one of social dominance.
Miller said he’s still in awe of the scale of the data. While getting his PhD, he spent two years studying honeyeaters in Australia and recorded about 400 interactions. The network of feeder watchers can generate that much data in a matter of hours or days.
The data set continues to grow as more birders report back to Project FeederWatch, and Miller expects it to prove useful not just in ornithology, but also in mathematical disciplines that study complex rock-paper-scissors-type competition and interaction.
Most interactions between birds end in a quick retreat, not combat. A widely recognized hierarchy helps birds avoid what could be very costly fights.
“If it’s the middle of the winter and you’re a little chickadee barely scraping by — you’re smaller than a couple fingers balled up and it’s 10 degrees outside — the last thing you want is to get blasted by a woodpecker with its bill,” Miller said. “It’s just gonna suck.”
Body mass is generally a good predictor of bird dominance, but woodpeckers dominate even some birds that outweigh them. “They punch above their weight because they spend their lives hammering on trees,” Miller said. “Their entire morphology is built to enable striking hard objects. So another bird is really not an issue for them.”
The most chaotic birds overall are probably the goldfinches and their cousins the pine siskins, Miller said. “They show up in flocks and they get in tons of squabbles both with themselves and everybody else.”
A small minority of bird rivalries are too complex for a simple ranking. For example, the house finch almost always dominates the purple finch, and the purple finch almost always dominates the dark-eyed junco, but when house finch and junco face off directly, the junco often dominates.
These tangled interactions are more common among invasive species such as the house finch, which is not native to the eastern U.S., Miller said. He speculated that these birds haven’t had millennia to find a clear place in the pecking order.
The database didn’t include interactions beyond the bird world. But if it had, experts say the data would have revealed the true king of the bird feeder: squirrels.
“Birds are made to fly — they’re light,” Miller said. “Squirrels just are way bigger, way freakier. They’ve got teeth. They’ve got claws. A bird is not going to take any chances near a squirrel. Squirrels will eat a bird no problem.”
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Illustrations are based on photographs from Project FeederWatch, a project of the Cornell Lab of Ornithology and Birds Canada.