By Clay Christensen

The other day, my neighbor Heather stopped me to ask some bird-related questions.

Lots of people I meet have questions about birds, and that’s great! It makes my life interesting.

Heather wanted to know why we see different birds in the winter than we do in the summer.

I said something about many of the summer birds being insectivores, insect eaters, and that there aren’t many insects around in the winter. And then there’s the issue of the COLD! That’s a factor that persuades many species to fly south (think snowbirds!).

But I also wondered what other elements are at work defining the different populations of species we see in different seasons.

As I often do, I turned to one of my books about birds, “The Birdwatcher’s Companion: An Encyclopedic Handbook of North American Birdlife,” by Christopher Leahy of the Massachusetts Audubon Society.

I looked up “Food Preferences” and found quite a list describing what different birds like to eat. I’ll share it with you in alphabetical order.

First there are the Carnivorous, flesh-eating birds like hawks, owls and shrikes. There are members of these families around all year. Some of them shift ranges in the winter, but most hunt in the same area winter and summer. We found evidence of a shrike’s handiwork on the Christmas Bird Count one year: the body of a chickadee wedged into the fork of a tree branch, the shrike’s larder.

Next are the Euryphagous birds, tolerant of eating many kinds of food. You’ll recognize these: gulls, starlings and, especially, crows! I’ve seen a crow trying to subdue a shrew by whacking it against the ground…tenderizing?

The Frugivorous birds are fruit eaters. An example is the tanager. There are some trees and bushes that retain their fruit into the winter, but I would imagine that it’s hard and not very filling.

The Graminivorous birds are eaters of grass. I think of grazing Canada geese. When I worked in an office building, I used to watch them nibbling on the lawn, gathered in the patches where the sun was reflected, melting the snow. Grass eaters would have difficulty getting much food after the snows have accumulated.

The Granivorous birds feed on grains or other seeds. These include ducks, geese, doves, blackbirds and finches. The last three species listed are frequent feeder visitors.

The Herbivorous birds prefer plant food. Leahy lists ptarmigan and grouse. The ptarmigan is found far north in Canada, so you won’t see them in your yard. The ruffed grouse can show up in Minnesota.

Insectivorous birds eat insects. This includes members of the flycatcher family, swifts, and to a degree, hummingbirds and kestrels. I couldn’t believe that hummingbirds could eat insects. I thought their bill was like a straw for sucking up nectar.

And then one day I saw a hummingbird open its bill. That answered the question! This is the food source that is most affected by the winter months. There aren’t many insects flying in the winter.

Monophagous birds are tolerant of only a single type of food. The example given is the Everglades kite. It eats only apple snails. When that population crashes, it affects the kites. This food source doesn’t apply to Minnesota, and the Everglades don’t get snow very often.

Nectivorous birds are nectar-eating. This includes the hummingbirds, orioles and occasionally, warblers, tanagers and finches. These birds are affected by the cold because there aren’t many flowers producing nectar in the winter.

Piscivorous birds eat fish. We have osprey, belted kingfishers, red-breasted mergansers and double-crested cormorants. This food category becomes endangered when the streams and lakes freeze over and the birds can’t dive for fish.

The last category is Stenophagous birds. They are tolerant of only certain forms of food. The brant, a goose-like bird from far northern Canada favors eelgrass. Woodcocks eat only earthworms. Since earthworms dig deeper in the winter, woodcocks would have a hard time finding food.

So, cold and snow affect many of the food choices that birds prefer.

But there may be other reasons we have a different cast of birds from winter to summer.

As we know, some birds migrate north in the spring. Often, it’s to build a nest in an area with lots of insects, like northern Minnesota for example. Many species are loyal to a nesting area and return there year after year. That’s called nest site fidelity.

By the same token, many birds migrate south in the fall. And there are areas in Central and South America where certain species congregate for the winter. There must be food and decent weather for those that make the trip.

Clearly, food availability is a big factor in where birds spend their time. Another is their traditional breeding area, where they can find nest sites and safety.

I look forward to Heather’s next question.

Clay Christensen lives in Lauderdale and regularly writes on birding for the Bugle.

Photo cutline: Northern Shrike. Photo by Ellen Lowery.

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