Craig Benkman’s 40-Year Fascination With Crossbills and Conifers

From the Autumn 2025 issue of Living Bird magazine. Subscribe now.

The rest of Craig Benkman’s life began on a snowy late-winter morning in 1982. As the first-year graduate student prepared to attend a seminar on ecology at the State University of New York at Albany, a classmate burst into his office with an urgent message: “Craig, Craig! There are crossbills coming to the ground outside!”

Benkman’s heart leapt. For months, he had searched around the Hudson Valley for the strange red finches, thinking they could be a perfect study subject for his dissertation. But so far, he’d had no luck finding any crossbills.

When he proposed studying the birds for his PhD, he knew it wouldn’t be easy. Red Crossbills and White-winged Crossbills, so named for the overlapping tips of their bills, are notoriously nomadic, wandering vast distances across North America’s remote evergreen forests in search of their only food source: the seeds of conifer trees, such as spruces and firs and pines. 

Unlike other birds that reliably nest in the same place year after year, crossbills will breed anywhere and at any time—even in the dead of winter—so long as they find an abundant supply of conifer seeds. All the while, they remain high in the treetops, making crossbills notoriously difficult subjects for ornithological research.

One faculty member on Benkman’s dissertation committee simply laughed at the thought of studying the birds. 

“I kind of got discouraged,” Benkman says. “I almost quit.”

Still, Benkman was convinced that crossbills had potential. That same dependence on a single, unreliable food source that made the finches so tricky to study also raised a host of fascinating questions to explore: How had the birds adapted to the challenges of accessing conifer seeds? Why did different crossbills have different bill shapes? 

So when Benkman’s classmate informed him of the crossbill flock on campus, he didn’t hesitate. 

“A group of us said, ‘No class today!’” recalls Benkman. By the end of the day, Benkman had netted about 10 Red Crossbills—more than enough to probe how the curious finches carve into conifer cones. 

“I thought, ‘Well, I guess I’m going to study crossbills!’” he recalls.

And so he did—for the next 40 years.

Over a decorated research career that has netted him honors from the American Society of Naturalists and American Ornithological Society, Benkman’s influential work expanded not only how ornithologists understand crossbills, but also how evolutionary biologists understand the relationship between species and their environments. He chronicles his life’s work studying the finches of the Loxia genus and more in his thorough and wide-ranging book Crossbills and Conifers: One Million Years of Adaptation and Coevolution, published in summer 2025 by Pelagic Publishing.

“[The book] touches on so many different dimensions of what we think of in terms of avian biology and ecology and evolution,” says Irby Lovette, director of the Cornell Lab of Ornithology’s Center for Biodiversity Studies. Lovette says reading about Benkman’s work on crossbills is almost a crash course in ornithology. “It’s like everything in one bird.”

Starting with that one snowy day in Albany, Benkman made his life’s work out of chasing crossbills from New England to Canada’s Maritime Provinces and out west to the Rocky Mountains and isolated South Hills of Idaho. Along the way, he developed fascinating insights into the relationships between birds and their habitats, challenged traditional notions about how bird species and their food sources evolve, and even discovered a new species of crossbill.

Uncovering the Crossbill’s Seed-Eating Secrets

After Benkman captured his first crossbills, he shuttled them to a makeshift aviary on campus. In the wild, it would be impossible to watch crossbills forage at the level of detail necessary to understand how they efficiently slip seeds from cones. But from behind a one-way mirror in the aviary, Benkman had an unprecedented close-up to the subtleties of feeding crossbills.

“The birds are so tame in captivity,” he says. “Once you put them in a cage, they’ll start feeding on cones within a couple of minutes.”

He spent hundreds of hours observing the Red Crossbills forage on amply provided pine cones—watching and taking notes as they contorted and flipped every which way to extract and husk seeds in seconds—before releasing them back into the wild. 

“More than once, I had to catch myself from clapping in admiration at what these feeding birds could accomplish,” Benkman writes in his book.

Benkman’s front-row seat in a lab aviary was perfect for understanding the details of crossbill feeding.

But to understand how the birds interact with their environment, he needed to venture out into the vast boreal forests that crossbills call home. He scoured the outer reaches of Ontario, Quebec, and New England for flocks of White-winged and Red Crossbills, even skiing down snowy forest roads on frigid midwinter days. 

How Crossbills Crack Open a Cone

Upon earning his doctorate in ecology in 1985, Benkman authored a series of papers that greatly enriched the scientific literature on crossbills. Across seven studies, he explained how crossbills use their elongated bills to pry open tough cone scales; discovered that a crossbill’s crossed bill was essential for consuming large amounts of conifer seeds, but a hindrance to eating other kinds of seeds; and described how the small bill of the White-winged Crossbill makes it well suited for exploiting tiny spruce and tamarack cones, while the larger bills on Red Crossbills can more easily break into hefty pine cones.

Along the way, the once-mysterious birds became more familiar to Benkman, both scientifically and personally. He began to feel as though he knew the crossbills as well as they knew themselves—their personalities, tendencies, and whims. 

“It’s kind of like bonding with a dog,” he says. “Being able to feel almost at one with an organism is a marvelous thing.”

Happening Upon An Evolutionary Classroom in the Idaho Hills

In subsequent stints as a postdoctoral fellow at Princeton University and the University of British Columbia, Benkman continued to build his bond with crossbills as he explored how they adapt to their environment. But after accepting a faculty position at New Mexico State University, he found himself surrounded by desert, far from his familiar finches.

“I wasn’t convinced I was going to continue to study crossbills,” he says. “I started thinking about studying lizard communities.”

He still had time to explore one last hypothesis, though. Benkman suspected that since crossbills harvest millions of conifer seeds every year, the conifer trees might in turn be adapting to better defend their seeds from predators. He wondered about a coevolutionary arms race—two species, a bird and a tree, becoming increasingly intertwined as they adapt in response to one another.

But studying his hunch would be complicated by squirrels. Across the Red Crossbill’s range, red squirrels are seemingly everywhere, and they are voracious cone predators. Benkman suspected that in the presence of squirrels, any crossbill-induced adaptations would likely be few and far between.

To observe conifer trees armed with defenses specifically against crossbills, Benkman would need to find a swath of forest free from squirrels. He pored over red squirrel range maps and local bird surveys for clues.

After a few failed efforts, a conference in Boise in 1996 gave Benkman a chance to visit another potential site: the South Hills, a small island of mountains rising from southern Idaho’s Great Basin.

It was a long shot. 

“No ornithologist had ever suggested anything special about the crossbills in the South Hills,” Benkman writes. But upon arriving in the forest, he was immediately struck by the abundance of crossbills that appeared like Reds, with large bills and strange calls. The crossbills fed with glee atop lodgepole pines, and there was not a squirrel in sight.

“It was no understatement that I was euphoric,” Benkman writes. He had found a living evolutionary laboratory. And if the South Hill crossbills were as different as he suspected, he may have discovered a new species.

Over the decades that followed, Benkman—and a bevy of graduate students from New Mexico State and the University of Wyoming, where Benkman was hired in 2004—examined the South Hills and their crossbills from every angle. Approaches ranged from the high tech—like sequencing portions of crossbill DNA—to the creative, including snipping cones from unreachable branches using 30-foot-long clippers, and even using dental equipment to make molds of the insides of the birds’ bills.

At every turn, the research confirmed Benkman’s initial suspicions. The cones in the South Hills were unusually large and had unusually thick scales at their outer ends, where crossbills prefer to feed—a clear sign of tree evolution driven by crossbills. Accordingly, the local South Hills crossbills had abnormally large bills and, unlike typical roving crossbill behavior, tended to stick around the mountains year-round. When birds from other crossbill lineages wandered in, they typically moved on quickly after finding the hefty lodgepole pine cones that local birds were far better at harvesting. 

Benkman and his collaborators discovered that the interloping crossbills rarely bred with the Idaho natives, making the South Hills birds more and more distinct as they continued to adapt to their own unique environment and food. The local crossbills even had different vocalizations than Red Crossbills elsewhere in the West. 

These findings indicated to Benkman that the finch was evolving into a new species. The proposed name for the new bird was Cassia Crossbill, after the county in Idaho where it resides; its Latin species name, sinesciurus, means “without squirrels.” 

In 2017, the American Ornithological Society’s North American Classification Committee accepted Benkman’s proposal. After a career full of discovery, he had his crowning achievement—not that Benkman is one to boast. 

“I’ve been privileged just to kind of bumble along and answer questions that, ‘gosh, this seems interesting—hopefully other people will be interested,’” he says. “In some cases, other people were interested.”

With Benkman’s discovery of the Cassia Crossbill, the once-overlooked South Hills area became a prime birding destination, with birders eager to add a potential new species for their life lists. A recent study by an economist at Mount Holyoke College documented that wildlife tourism in the region has boomed since the Cassia Crossbill was designated its own species, with the annual number of birder visits nearly doubling over the last decade.

“With my birder hat on, I’ve made sure that I’ve seen them,” says Lovette, who planned a trip to Cassia County specifically to see Benkman’s birds.

Evolutionary biologists were also fascinated by the ways Cassia Crossbills have shaped their environment. 

“As a scientist, I love it because it’s a little bit of a window into how species form,” Lovette says. “It’s kind of the textbook example of coevolution between birds and their diets.”

In fact, it’s too good of a textbook example. When Lovette edited the Cornell Lab’s Handbook of Bird Biology ornithology textbook, he had to ask contributing authors to avoid using so many crossbill examples. 

“[The crossbill research] is not just about dietary ecology or foraging—it’s also about evolution and about contact calls and coevolution and community ecology,” Lovette says.

Benkman retired as a University of Wyoming faculty member in 2022. But even after four decades spent chasing and studying crossbills, he’s not done exploring the Loxia finches. Familiarity has not bred contempt—far from it. 

“Take an astronomer: The more they learn about space, the more they marvel at it when they look up,” Benkman says.

Next summer, he will be waiting in his home near Fort Collins, Colorado, for the Red Crossbills to return to the forests nearby. The uncertainty of his younger self is gone. He knows the crossbills will come back. 

“I can’t wait,” he says. “They bring me tremendous joy every time I see them.”