For the Birds Radio Program: Winter Bird Movements
Now that winter is settling in, a few birds are hunkering down for the duration. But in this case, “the duration” isn’t necessarily until winter ends. To endure a northern winter, birds may adapt to changing conditions with changes in diet or by finding new roosting spots within the same territory. Sometimes they move on to new areas. Their movements trend pretty much southward through January, but there are exceptions even to that. Great Horned Owls are mostly on winter territories now—areas where they can count on a reasonably steady food supply and a few thick conifers where they take refuge during the day, out of view of harassing crows and jays. If they deplete their winter prey in one area, or if an ice storm knocks down their favorite tree, they move on. Cardinals and northern sparrows such as juncos may settle into a neighborhood with good feeders or natural foods for the entire winter. But if weather conditions grow too harsh, or if the diet isn’t supplying necessary nutrients, they move on. Sometimes they leave for reasons we don’t understand. Some birds never settle in anywhere. Robins and waxwings form large, gregarious flocks that travel together searching for and pigging out on winter fruits. A wandering flock may notice a crabapple tree or mountain ash, richly laden with fruit. The birds descend and devour it all in a matter of minutes, hours, or days, and then wander off in search of another bounty. The many eyes in a flock increase their chances of detecting sustaining food and potential dangers. Waxwings even help one another digest their food. When I rehabbed a Bohemian Waxwing one winter, I noticed that 10 or 15 minutes after it swallowed a mountain ash berry, the berry came out the other end, still intact. Outside, the waxwings passed a berry back and forth, up and down a line of birds, before one swallowed it. When I started rolling the berries between my thumb and index finger to soften them first, the waxwing could digest them much better. Apparently their charming habit not only helps cement their social bonds, but also helps them digest their food. Redpolls, crossbills, and other winter finches also move in large, hungry flocks. We used to have so very many Evening Grosbeaks in northern Wisconsin and Minnesota that it seemed like they were settled in, though banding studies showed that a great many of them only remained in a neighborhood for a few days or even hours. But there always seemed to be as many birds coming as going, so the numbers seemed rather constant. Evening Grosbeaks have declined grievously throughout their range, especially in eastern North America, since the 1980s. The ones that remain are still wanderers. A flock of six visited my mother-in-law’s yard in Port Wing, Wisconsin, on November 14. They were there all day, feeding at her sunflower seed tray feeder, in her spruce trees, and on some fluttering birch seeds, and then vanished. The joy and the frustration of winter birding are tied to these unpredictable movements. A Northern Shrike may visit our yard one day, scaring off all our feeder birds, but it will quickly move on, requiring an element of surprise to successfully hunt observant little birds. Rare songbirds can also turn up at a feeding station in winter, especially during November and early December. Summer Tanagers, Baltimore Orioles, and Pine or Cape May Warblers have all appeared in northern Wisconsin and Minnesota in the past. An Inca Dove turned up in Two Harbors, Minnesota, for a few weeks in December 2007. Winter birding is like a box of chocolates. You never know what you’re going to get, but even when the box is almost empty, every single one is sure to be sweet.