A Cooper's hawk family album -- Wisconsin Natural Resources magazine -- February 2000

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February 2000

The author with the male parent Cooper's hawk. © Jim Nicewander

The author with a new friend – the male parent Cooper's hawk.

© Jim Nicewander

A Cooper's hawk family album

When a family of seldom-seen "Coops" takes up residence in a Plover backyard, an adult student takes notice.

Jim Nicewander

Beneath the camouflage | Watched like hawks
Hunting and feeding activities | What we learned
Success on the wing

The combat would fit perfectly in a TV show with an ugly title like Nature's Death Battles: Four young Cooper's hawks are ganging up on a gray squirrel in a vicious struggle in the matted leaves under the oaks and maples. The birds are about six weeks old and almost as big as crows, so their prey is in the fight for its life.

There's little cover except for a brush pile a foot or two high running the length of the woods. The squirrel runs toward a rail fence at the trees' edge, but a hawk flaps past him and blocks that path. He darts back toward the brush pile, and another Cooper's responds accordingly.

The birds seem awfully young to be hunting cooperatively, but they're doing well at containing the squirrel, who's proving to be a formidable foe. He's fending them off by biting, jumping, kicking, scratching and flailing away with everything he's got.

That fierce defense – and his attackers' apparent inexperience – are all that's preventing the squirrel from becoming a meal. When the hawks do engage him in direct "talon-to-claw" fighting, he appears to inflict more wounds than he receives.

The brawl intensifies, and the birds try to move in even tighter, right into the thrashing teeth and claws. In that instant, an adult female hawk – "Momma Coop" – swoops into the woods about a yard off the ground and right through the fight. Her abrupt intervention breaks up the battle, and the squirrel seizes the opportunity to escape into the brush pile.

The adult Coop continues her flight into a tree overlooking the brush, within just a few yards of a human observer who is covered by camouflage. The bird seems to pay no attention to him.

Three of the juveniles join the adult in an adjacent tree. After a couple of minutes, she swoops down onto the brush pile, flushes out a chipmunk, catches it with her powerful talons and flies off; the three closest juveniles follow her.

The fourth young hawk, a male, has been watching from the ground. He wings his way over to the brush pile, not far from where the adult had just caught the chipmunk. He picks at the sticks a while and flushes out another chipmunk, a less difficult adversary than the squirrel. The hawk catches it with little problem and begins tearing it apart and eating it on the spot.

Success on the wing

For a long time we knew less about Cooper's hawks than we did about many other North American raptors. The birds are relatively secretive in their habits and habitat, making them more difficult to study than red-tailed hawks, American kestrels, or even bald eagles.

Our knowledge about Cooper's hawks has been enrichened by the research of Dr. Robert Rosenfield, a biology professor at the University of Wisconsin - Stevens Point, and his colleagues. Rosenfield's primary research partner over the years has been fellow scientist John Bielefeldt of Sturtevant. Their study of Cooper's hawks in Wisconsin began in 1980, and it's been so successful that other researchers in other raptor studies have adopted many of their methods.

The project began with banding birds – about 2,400 individual hawks to date. At the time they are banded, the adults are weighed, the wing and tail feathers are measured, eye color is recorded (an approximate index of age in the males), and the molt (sequence of replacement of worn-out feathers) examined. The records are compared with data on the hawks' offspring. The study has yielded a mother lode of data, and since the start of his research, Rosenfield has had a part in about 30 published papers on the species.

Rosenfield's 20-year project is by far the longest on-going study of Cooper's hawks, and one of the farthest reaching: He has collaborated with fellow researchers in northwest North Dakota and in British Columbia, where populations of the hawks rival those in Wisconsin.

"Ultimately, we're trying to find answers to questions like what environmental or ecological factors influence the hawks' breeding," says Rosenfield. "What things contribute significantly to their success? In this research, I see myself as sort of a sleuth trying to uncover some answers to those things."

His detective work has yielded some important results. One of Rosenfield's most recently published papers presented data indicating that hereditary factors significantly contribute to which Cooper's hawks became breeding birds. That irrefutable determination of genetic links, as compared to purely environmental causes and effects, is an unconventional finding in the world of raptor ecology.

As his study has progressed and the data has taken on more long-term significance, Rosenfield has become convinced that the Cooper's hawk – declared as a threatened species in 1979 – is not in trouble in Wisconsin. As he and Bielefeldt put it in a recent paper, "The Cooper's hawk may...be one of the commonest diurnal [daytime hunting] raptors in Wisconsin...the Cooper's hawk has retained or possibly regained – we do not know which – its former status as one of the state's most numerous nesting hawks."

Their research was instrumental in getting the Cooper's hawk downgraded from threatened status to a "species of special concern" in 1989. To motivate students, Rosenfield brings his studies right into the classroom – following in the footsteps of renowned researcher Frederick Hamerstrom, who was not only Rosenfield's academic advisor, but his mentor as well.

One of the great things about our research is how it provides so many educational opportunities for our students, especially our undergraduates," Rosenfield says. "It's exciting to get them enthusiastic about helping us work with the data we are amassing.

Because our Cooper's hawk research is known both internationally and locally, the UW-Stevens Point campus benefits directly when our students participate in it. They help the project and for many, this is their first real contribution to hard science; it helps kick-start them into careers as scientists. It motivates them in invaluable ways that their reading and my teaching can't accomplish," he says. "That educational part of it all gives me unspeakable gratification," Rosenfield says. "It makes our projects much more valuable than if they were just research."

Two of the other juveniles return and perch in branches about 25 feet away from the male and his meal. He continues consuming his catch, stopping only to mantle – raise his wings like a shield to hide and protect his prey from other birds.

The young Cooper's hawk finishes off the chipmunk and flaps to the top of the brush pile. Using his beak, he removes the chipmunk residue from his talons and feet and then cleans his beak by brushing it against some sticks.

With that completed, he flies out of the area, followed by one of the two remaining birds. The last one glides down to where the male had finished eating and pokes and scratches around the bloodied twigs and leaves. When she finds nothing that holds her attention, she flies off toward the others.

Beneath the camouflage

The human observer in this real-life drama was not a research scientist, but me – a decidedly unscientific school administrator who just happened to be in the right place at the right time. The right place was not wilderness, but merely the woods on our two-acre parcel in a subdivision in Plover, in the heart of Wisconsin.

I had not gone looking for the hawks; they just found likable habitat, and I happened to be there. I'm no Cooper's hawk expert. Indeed, my sole previous mention had been a conversation with my father back in the 1950s on our farm in Waupaca County.

UW-Stevens Point student Carrie Walczak with a pair of Cooper's hawks. The larger bird on the left is the female.
© Jim Nicewander

As a kid back then, I spent many summer hours watching large, soaring hawks ride thermals over our fields. They were redtails, and nearly everybody called them "chicken hawks," though my dad didn't think those big hawks were the chicken thieves. He said the real robbers were the "Coops." But he said they hadn't been around our place in a long, long time, and I never did get to see one on the farm.

More than 40 years later, here I was, watching a whole bunch of Cooper's hawks. It happened only because a series of fateful occurrences converged that summer:

As fate (version 1) would have it, a second semester course called Raptor Ecology had been offered at UW-Stevens Point, right up the road from my place. It was all about hawks and other Wisconsin raptors, so I signed up as a middle-aged, non-traditional student, just for the excitement of learning some science to go with my memories.

As fate (version 2) would have it, halfway through the semester, we spotted a couple of hawks hanging around our place. How fortuitous: having some real live birds to observe as I studied them in school.

As fate (version 3) would have it, we learned that the raptors in our woods were Cooper's hawks. Great, I'd finally get to see some authentic chicken hawks!

And then as fate (version 4) would have it, my professor was Dr. Robert Rosenfield; not only a gifted teacher, but a world-recognized researcher and authority on Cooper's hawks.

The hawks in our woods had a nest in a large white pine about 100 feet behind the house, and they hatched five young ones in it. The parents and offspring all became part of Dr. Rosenfield's research when he trapped and banded them in late June. Then, when the little ones fledged and left the nest in mid-July, we thought we had seen the last of them. However, we soon found out they had staked a claim on our woods as their own homestead, and stayed until early August.

Dr. Rosenfield said we had a unique opportunity to observe immature Cooper's hawks for an extended period, something that few people get to see. We made more than 80 observations of the young hawks' activities during their 3½ -week stay.

As the hawks grew in age from about six weeks to ten weeks old, their loud and frequent calling would trigger our observations. We would hear them outside and I would don some camouflage and slip out to watch them.

Watched like hawks

The young Cooper's hawks displayed a wide variety of behaviors, ranging from solitary resting to dynamic group activity. Here's a representative sample of the kinds of things we saw.

Banded, weighed and measured, two of the five Cooper's hawk nestlings are ready to be returned to the nest.

© Jim Nicewander

Gender differences: The juvenile hawks did not all look alike. I remembered from class that Cooper's hawk females are about one-third larger than males. The males in our group were not only smaller, but their coloration was noticeably different. While juvenile Cooper's typically have vertical streaking on the breast, markings on these males appeared significantly more pronounced than on the females.

Absence of adult hawks: Some studies have suggested that after fledging, young Cooper's hawks periodically get fed by the parents. We never saw an adult bird feeding a youngster.

We only saw an adult with the juveniles two times. The first instance I've described, and a second time when two young hawks aggressively chased one another through the woods, calling loudly at each other. They landed on the same branch and began pushing and jostling one another, barely keeping their balance. The adult female flew to the tree the young hawks were in, landing on a branch just above the battling juveniles. They immediately stopped fighting and flew off as soon as she touched down on her perch.

Frequent flyer exercise: Routine behavior for the young hawks during most of our observations involved groups of the birds just flying back and forth within the woods. The hawks swooped into the woods, flying only a yard or so above the ground, rising above the bushes and descending again, following the contours of the ground cover. One hawk and then another would take the lead, all of them staying within a couple yards of each other.

When they landed, they frequently settled for just a few seconds before taking off again. There was usually much loud "eeeee – eeeee" calling among them, and for long periods, individual birds would not get more than four or five yards away from one another for more than a few seconds during these maneuvers.

Physical contact between hawks: At times, the hawks physically challenged one another. In one instance, two females stayed right beside each other, less than a yard apart. They hopped from branch to branch as a pair, first one and then the other initiating the move. There was frequent and considerable physical contact between them, with a great deal of wing flapping and pushing at each other, though the behavior did not appear hostile.

Hunting and feeding activities

We observed many instances of the juveniles trying to catch prey animals. Some incidents revealed that the birds were still learning; other times they showed a remarkable adeptness at catching food.

Hunting postures: Typically when hunting, the young hawks firmly gripped a branch with both feet, sitting erect with the head held up. In this position, the hawks frequently turned their heads side-to-side and up-and-down.

One of the juveniles varied its hunting posture by hunching over in a vulture-like stance, taking on a "skulking" appearance, as if trying to get a better view of some prey.

A rough landing: One juvenile hawk flew into a dense thicket of branches after seeing a squirrel. Without sufficient space to completely clear the branches, one wing got caught and the bird could not keep its balance. It tipped off the branch and had to resume flying as it fell toward the ground.

Group hunting: In another hunting incident, four of the immature hawks group-attacked a chipmunk. They lunged at him repeatedly, but not in a well-organized attack. After a minute or so, one bird caught it, and flew out of the observation area with the chipmunk; the other birds following.

Male hawk mantling over prey: In one of the most interesting observations, one of the males swooped down to the ground, and after a flurry of activity, flew up to a large branch overhead, carrying a chipmunk. He was quickly joined by two of his female siblings, one landing on his branch and the other right above him.

Those two birds called frequently and gradually worked their way closer to the male, which had begun eating his catch. When approached within a yard or so, he mantled over his meal until they backed off. One of the females finally flapped right up next to him and did not back off. Instead, she moved even closer, with physical contact and intense calling by both birds. She quickly retreated, but the male did not resume eating until she had turned her back to him.

Two females sharing food: Mealtimes weren't always contentious. In one instance, two female juveniles flew into the observation area, landing on low branches right above the brush pile. One swooped down to the brush, and after a brief commotion, hopped up to the top of the pile with a chipmunk.

The other hawk flew down and landed about a yard from the bird with the food. That hawk with the chipmunk began eating it, and the other moved closer. The eating bird mantled over her food, but put down her wings when the approaching bird reached in and tore off a piece of the animal and ate it. The two hawks continued to alternate their feeding until the chipmunk was totally consumed.

What we learned

The opportunity to hang around juvenile hawks for a few weeks was exciting and enlightening. It helped me connect to my younger years on the farm and see some of the hawks' interesting behaviors. By the time it was all over, I appreciated just how lucky we had been to be in the right place at the right time.

And for the record, in our weeks of watching the Coops, not once did we see them take a chicken!