In a bird-eat-bird world, what's for dinner is a big deal. Eight species of hawks and owls are major predators in and around the Twin Cities. While their prey choices overlap in many cases, they manage that competition by being just different enough.
We host three species of owls here: barred, great horned and Eastern screech-owl, the latter two year-round. Cooper’s, red-shouldered, broad-winged and red-tailed are our common hawks, with red-tails around all year. We also have osprey.
If you were to invite them all for dinner, serving their usual diet, the menu should include birds from the size of fledglings to herons, rabbits, rodents, muskrats, squirrels, skunks, opossums, chipmunks, bats, house cats, snakes, frogs, toads, crayfish and various insects. And fish for the osprey.
Physical differences dictate food choices. Or perhaps it’s the other way round. These birds are built to hunt by day — perching, soaring, swooping, diving, hovering — or by flying silently through the night.
Cooper’s hawks are slim with narrow wings for fast flight, their long tails acting as rudders. They swoop into the yard, often low, always fast, scattering our feeder birds. Prey most often are robins, jays, starlings and flickers, all commonly ground feeders.
Red-tails and red-shouldered hawks hunt from perches or in flight. The difference? Red-tailed hawks are birds of open areas, red-shouldered are woodland hunters.
Broad-winged hawks also are woodland hunters, perching below the tree canopy, choosing amphibians as food more often than their hawk brothers.
Screech-owls, being small, often feed on bird nestlings and fledglings. They also take small mammals and insects.
Great horned owls eat the full menu, particularly mammals. They mostly have opossum, skunk and house cats to themselves.
Great horned owls also eat barred owls, which simplifies the competition angle for the latter: Find your own place to hunt small mammals, birds and amphibians or be hunted yourself.
Osprey eat fish. The pair I watch each year often choose koi. (How hard can it be to catch big, brightly colored fish in a cement pond? How expensive for the provider?)
Eyes are a particularly interesting hawk/owl difference. Owl eyes are proportionately large, allowing activity at night. Owl eyes are so large that the eye socket cannot accommodate muscles that would move the eye up and down, left and right. Owls must turn their heads to look around.
Hawks, relying on sharp vision, have eyes placed more to the sides of the head. Cooper’s hawks, for example, have a sight radius of about 240 degrees. Soaring hawks seek prey with eyes seeing 10 times the detail we see.
To find their niche in a highly competitive world, species that share a hunting territory must adapt in some unique way. Each bird in this case has evolved a different hunting strategy and a particular set of tools. That can be eyes, feet, feathers, prey preferences or hunting techniques.
In a competitive world, animals either evolve into a niche or the species dies. Even if that means you get to eat the skunks and toads.
Lifelong birder Jim Williams can be reached at firstname.lastname@example.org. Join his conversation about birds at www.startribune.com/wingnut.