Naturalist's Corner - Just Ducky

In this month's column, our guest is Janet Malotky, a bird watcher extraordinaire who was part of my 2022 Master Naturalist volunteer cohort. She is also a member of the Frontenac State Park Association. As an avid birder, she enjoys nothing more than getting outside, binoculars in hand, to revel in the amazing natural world around us. In this article, Janet breaks down how ducks are able to stay warm. This article first appeared in the December 2023 Frontenac State Park Association Newsletter. 

Bird Notes: Our December Ducks - and How They Keep Warm

Fall migration stirs a mist of melancholy, for while it’s exciting that our little friends come visiting on their way south, they don’t stay, and they’re trailing winter in their wake. Bird and bird species numbers continue to drop, and they stay low until spring.

A few birds, however, arrive from the north in late fall and stick around for a while to brave the fierce winter weather with us. We see rafts of them in December, bobbing in open water surrounded by ice. They’ll stick around for as long as they can find open water. 

Most of these are mixed flocks of Common Mergansers, one of our largest duck species, and Common Goldeneyes. They breed in Canada and Alaska, then fly south for the winter, mostly to large freshwater rivers and lakes in the United States, like the Mississippi and Lake Pepin. Some, especially Goldeneyes, also winter off the Pacific and Atlantic coasts. 

Common Merganser and Common Goldeneye
Image - Steve Dietz

Common Merganser and Common Goldeneye males are mostly white-bodied with some black on their backs. They have dark green iridescent heads that usually appear black, as in the photograph above, taken at Sand Point. The females of both species have warm brown heads and brownish-gray bodies. In addition, female Mergansers have jazzy crests of brown feathers on their heads (best seen on the far right center bird under the flapping male’s wing). In the photo, all the birds with orange-red bills are Common Mergansers. Two Common Goldeneyes can also be identified. The Goldeneye male, center left (facing right), has a round white spot just below and forward from his eye. The female is a few duck-lengths ahead of him, just right of center, also facing right and in profile. Her brown head is the same triangular shape as her mate’s. And of course, both Goldeneyes have golden eyes.

You may wonder how in the world these birds keep from freezing to death. The first part of the answer is that their bodies are thickly covered with down underneath their feathers, which traps an insulating layer of air next to their skin. In addition, they keep their feathers waterproofed by rubbing them with oil from special glands when they preen. Lastly, they (and many other birds and mammals) have a remarkable circulatory adaptation, a “countercurrent heat exchange system” that keeps their core temperature at a more steady state, while still keeping their feet and legs from freezing.

It works like this: The cool venous blood heading back from the feet toward the heart passes very close to the warm arterial blood leaving the heart toward the feet. The cool blood gets warmed up a bit as it passes the warm blood, so by the time it gets back to the heart it doesn’t cool the bird’s core down as much. At the same time, the warm blood heading for the feet gets cooled down a little bit as it passes by the cool blood. This is OK because, since the feet and legs are mostly bones and tendons, they don’t need to stay as warm. Because the feet and legs have very little insulation, there is less heat lost to winter’s chill than there would be if the blood was still warm.

Common Mergansers and Common Goldeneyes are diving ducks. Both species eat fish, aquatic invertebrates (mollusks, snails, insects and their larvae), and aquatic plants. Common Mergansers also eat frogs, small mammals, and birds, which they grip tightly with the serrated edges on their bills. This unusual bill feature has earned Mergansers their nickname: Sawbills.

Bald Eagles can frequently be seen hanging out at the edge of the ice where the ducks are fishing. Although eagles have been observed hunting and eating these birds, this seems to be rare. Mergansers and Goldeneyes are more vulnerable to predation when they are chicks. By the time they arrive in our park, they are fully grown, and their main concern when it comes to eagles is protecting their catch. Eagles are ready to filch a fish at the first opportunity.

And when you’re a duck trying to make it in a cold northern winter, you need all the fish you can catch.

Note: Membership information in the Frontenac State Park Association can be found here. Copies of and subscriptions to their marvelous newsletter can be found here.