What You Can See on Feb. 20

From Audubon’s Earth Almanac by Ted Williams and compiled in “Wild Moments,” edited by Connie Isbell, Illustrations by John Burgoyne, Storey Publishing, 174 pages. Winter Bluebirds Never are eastern bluebirds brighter than when fields and backyards east of the Rockies are draped in snow. The species had been drastically reduced -- mostly by starlings and house sparrows, which usurp their nesting cavities. But for the past 24 years, an effort by the North American Bluebird Society to popularize artificial nest boxes has produced spectacular results. As bluebirds surge back, more and more of them are wintering in the North, where they sustain themselves on fruit. During cold snaps they will roost in the boxes, sometimes in groups of a dozen or more. They eat all sorts of berries, but perhaps their favorite is cultivated winterberry holly. Collect berry-laden branches and push them into the snow. When bluebirds start coming, place some of the berries in a bowl and add mealworms (available in large containers from pet-supply companies; they’ll keep for several months in your refrigerator). Bluebirds will learn to take just the mealworms, a much more nutritious winter diet. Starlings and winter robins will gorge on the mealworms, too, and the robins will drive the bluebirds away, so you will want to buy or make a "selective" feeder. Cut a large rectangle in the top of an old birdcage, then place the bowl of mealworms on the bottom. When bluebirds start coming into the cage, place a board with a 1-and-3/4-inch hole over the rectangle. Although that's big enough for starlings, they're extremely reluctant to enter, and the larger hole will prevent bluebirds from getting trapped when ice forms on the edges. Place a twig between the wires three or four inches under the hole so the bluebirds can perch before exiting; otherwise they’ll get trapped. In early spring your mealworm-fed bluebirds will have a tremendous head start over all nesting competition. Snow Bunnies As the days dwindle down the fur of the snowshoe hare goes white; but, unlike the pelage of other mammals -- including, alas, our own -- it will get brown again in spring. If a hare goes white before the snow falls, it’s in big trouble because in bare hardwoods or black conifers it stands out like phosphorus in a night sea. The “snowshoe” part of its name derives from large, splayed hind feet that allow it to travel easily over snow. Throughout its range from Alaska, across most of Canada and our northern states, and down the spines of the Rockies and Alleghenies, few prey species are more abundant or subject to wilder population swings. In good hare years predators such as owls, foxes, fishers, and lynx thrive. But as hares proliferate they deplete their bark-and-twig food supplies, triggering a population crash that soon extends to their major predators. Snowshoe hares provide more evidence that what we all learned in biology class is wrong and that, for the most part, it’s prey that controls predators.