What’s a Northern Cardinal Doing at a Pile of Deer Guts? Chowing Down.

Northern Cardinals are not picky eaters. They forage everything from insects to flower petals, and they’ll happily visit feeders with a variety of seeds, especially black oil sunflower. Also apparently on the menu? Deer guts. 

More than three dozen bird species have been spied at piles of innards, called offal, thanks to a collaboration between researchers and deer hunters in Minnesota, who leave behind the organs after field dressing the animals they harvest. While many visitors are expected—corvids and raptors are first on the scene and often dominate the scavenging—other are more eyebrow-raising: Turkey Vulture, sure, but Wild Turkey? Also spotted.

“There is not a hunter out there that is surprised that scavengers are coming,” says Ellen Candler, a biologist who started the Offal Wildlife Watching Project in 2018 as a Ph.D. student at the University of Minnesota. But the guest list to the organ meat dinner party is long and varied, including elusive mammal and bird species like flying squirrels, gray wolves, fishers, and Northern Goshawks. And far beyond familiar carrion eaters, the avian roster includes American Robin, Eastern Bluebird, Mourning Dove—even American Woodcock. 

It’s not certain that every visitor dines on the viscera. Some may just be passing through. It’s also possible that species like American Goldfinch—one of the strictest vegetarians of the avian world—and Dark-eyed Junco are drawn not to the organs themselves, but to undigested corn and grains still inside, says project coordinator Grace Milanowski. “I don’t think people are thinking about if your stomach gets left behind.”  

But plenty of birds have been caught red-handed (or red-billed) tucking into the offal piles. Candler was initially surprised to see so many woodpeckers on the trail cameras set by participant hunters. Talking to birders, though, she realized that the woodpeckers and several other of the smaller documented species, including nuthatches and Black-capped Chickadee, are frequent visitors to fat-rich suet feeders. “It makes sense that they’re using this resource. It’s just like a big suet feeder,” she says. “Plus a little bit extra.” The lesson seems to be: Birds, like many wild animals, will take the calories wherever they can get them.

Candler, who grew up in a hunting family in southeast Idaho and is a hunter herself, knew first-hand that hunters have a long history of supporting conservation and are curious about the natural world. But her idea to enlist Minnesota hunters to help study gut-pile ecology was also pragmatic. “The community aspect started because I was like, well, I’m really interested in all of this, and I don’t have funding, but I want to collect a lot of data,” she says. The project now receives support from the state, through a fund built on lottery ticket sales, but it remains resolutely people-powered. 

More than 400 hunters have taken part in the project since its inception seven years ago, signing on to train a trail camera (their own or borrowed from the project) on their offal piles for one month and send in the results. Many participants were recruited through Minnesota’s Master Naturalist program, including Mike Lein, who has hunted with family and friends on a property in far northwest Minnesota for more than 40 years. “We didn’t pay much attention to birds before,” Lein says of the expeditions. He has been excited by what he’s documented, like Rough-legged Hawks “close up and personal” and Black-billed Magpies, whose range just reaches into Minnesota. 

With the hunters’ involvement, Candler says, the project has taken on a life of its own. “It’s morphed into: People are into this. And people have questions outside of my questions,” she says. One of Lein’s observations even informed a new direction for the research. His trail camera captured a bobcat playing with a mouse or vole “like a house cat.” Then he noticed Barred Owls catching rodents in the offal, too. The photographs suggested a more complicated food web: Could predators seek out gut piles not only for the organ meat but for live prey? Candler’s team decided to investigate, launching a pilot study this past fall to trap small mammals at a few offal piles. Next, they hope to install acoustic monitors in the field to listen in on the hunt. “That was unobserved behavior that we likely would have missed,” Milanowski says, if not for Lein’s sharp attention. 

With so many hunters participating—183 in the 2025 hunting season—the offal-watching team receives far more trail cam photos than they can handle alone. So the researchers turn once again to community science. Through a platform called Zooniverse, volunteers anywhere in the world can help identify species in the images. More than 10,000 people have contributed, including from as far away as Saudi Arabia and Russia. Any given photo set is reviewed by at least 10 volunteers, with the researchers verifying disputed IDs. It’s a robust and reliable system, Candler says—with a few reasonable tweaks: “We’ve combined crows and ravens,” she says of the oft-confused species. 

While it’s made up for in the volume of observations, relying on community science does have a few limitations. “If it was us going out to set cameras, we would take all of these other measurements,” Candler says. “Like what kind of trees are here? How big are the trees? What is the soil type?” Since setting the trail camera—and, crucially, retrieving it a month later, which could involve a long trek back to hunting grounds—is a significant ask of hunters, Candler keeps the procedure as simple as possible.  

The team also does not initiate conversations with participants about the dangers of lead bullets, which can poison birds and other wildlife through gut piles and has stymied recovery efforts of iconic species including the Bald Eagle and the California Condor. “Because it could be a controversial topic among hunters, it might impede our other basic questions,” Candler says. But she doesn’t shy away from the conversation when prompted: “If a hunter ever asks me, I’m very honest about what the research says in terms of the dangers of lead ammunition for scavengers, particularly birds.” 

With the trail camera photos recently returned from the 2025 hunting season, Milanowski says this is the most exciting time of the project for her—and for the volunteers who identify species in the images. (Photos from this past season should appear on Zooniverse very soon.) Last year the team added 10 new species to the list of documented gut pile visitors, and they have a few white whales: No camera has yet captured a mountain lion, lynx, or wolverine. “It just goes to show we need more surveillance, because there’s more happening than what we know about,” Milanowski says. And there are always more questions to pursue. The team is currently working out how to measure how long the gut piles persist on the landscape. They’ve also yet to crack a popular query from hunters: Which organs get eaten first? 

Candler, who continues to co-lead the project despite relocating to the University of Alaska Fairbanks, would love to see the project expand to other states. “A white-tailed deer harvested in Minnesota is going to be a lot different than a white-tailed deer shot in Louisiana, right? They’re very, very different habitats and weather. I’m curious about how scavenging happens in those different environments,” she says. Although, for now, the project’s funding only covers Minnesota, Milanowski says they do hear from hunters in other states wondering if the team would be interested in their photos and observations. “Feel free to send them to us. We want to see it,” Milanowski says. “We are enthusiastic gut researchers.”