The eagle in winter

As I sit on a red cooler working a waxworm on a jig sixteen feet below the Birch Lake ice, I hear a piercing scream from somewhere high in a tree along my shoreline. Of course it’s a bald eagle, and I wonder what he or she is doing still here in the middle of winter, while the lakes are frozen solid and pickings are slim at best for the fish that make up most of eagles’ diet. Eagles are found just about anywhwere in Wisconsin these days (see the accompanying map from the DNR), but it’s not obvious what keeps them here up north in this season.

I know that if someone were to empty a bucket of chubs or shiners on the ice, the eagle would soon find and devour them. And if I were to leave a few of the bluegills I catch lying in the snow, the eagle would notice and take action. It’s a form of what is sometimes called wake hunting, the way flocks of gulls on Lake Michigan learn to follow in the wake of commercial fishing boats and scavenge for any discarded fish or entrails.

I’ve observed this wake hunting by eagles in the open-water season. If, for example, I release a perch or bluegill that I’ve injured in unhooking, and it floats up and struggles on the surface, chances are good that an eagle will spot it. And if the fish drifts beyond a certain distance from my boat, the eagle will silently circle, swoop down, and snatch it in its talons. It’s my experience that an eagle won’t pick up the fish if I’m watching; only if my back is turned. If I want to observe the spectacle, I have to watch furtively, from the corner of my eye.

But in winter, a few random minnows and fish on the ice won’t provide a survivable diet. So chances are that any Birch Lake eagles will make journeys to someplace where the water is open for their fishing, like below the Rainbow Dam about 13 miles away. We also see eagles along town roads and state and county highways, feasting on road-killed deer, ripping off pieces of meat with their sharp beaks. But in this season most of the eagles congregate farther south, on the Wisconsin and Mississippi rivers where the water stays open year-round.

Of course, it’s still plenty cold in those places, but the eagles are adapted, and the secret is in their feathers. Close to their skin lies a layer of down, soft and fluffy, that traps air to form a kind of insulation, akin to the down or fiberfill in the winter coats we wear. Over that are contour feathers that give eagles their basic shape. These feathers overlap one another like roofing shingles, only the edges exposed directly to the cold air. Those edges are waterproof and keep out snow and moisture.

The eagles keep those feathers clean and properly aligned through preening. That process includes treating the feathers with oil from a gland above the base of the tail. Eagles also keep warm by puffing up their feather to trap air so that their bodies can heat it. And they tuck their feet under the feathers and close to their body to keep them warm. All this is why we can still enjoy eagle-watching in winter, and why I get to hear those high-pitched calls as I concentrate on my ice-fishing jig rod.