For the Birds Radio Program: Autumn
Spring and autumn are transitional seasons, with dramatic weather swings that in a three-month period change a northland summer, with highs in the 90s, to a northland winter, with lows down to 50 below zero. The transitions aren’t normally so extreme, but do give us some pretty clear insights about the coming season. As a matter of fact, the biggest snowstorm ever recorded in northern Minnesota fell on Halloween.
Even those of us who exult in northern winters have to brace ourselves for the coming season. We protect some of our garden plants, bring in birdbaths and picnic tables, check our weatherstripping, and pull out our long johns and winter coats.
Birds who don’t hightail it out of here for the duration are also battening down the hatches. Adult birds never sleep in nests except during the nesting season when they incubate their eggs or tiny nestlings, but many adult birds do sleep in cavities. Woodpeckers are the prime builders of the bird world, creating new cavities fairly often, leaving the old ones for other species that aren’t endowed with carpenter skills and tools. Bluebirds, brown creepers, Saw-whet and Boreal Owls, and lots of other species use old woodpecker holes. Chickadees and nuthatches sometimes appropriate an abandoned Downy Woodpecker cavity, but these species like trying their own do-it-yourself projects. They may not be endowed with a woodpecker’s hammer, but their tiny beaks can pack a wallop to excavate holes big enough to accommodate their little bodies. Chickadees are the Norwegian bachelor farmers of the bird world, and don’t like to get too close to other chickadees, so they each seek out or build their very own roost holes. Although Pygmy Nuthatches sleep in communal roosts, Red-breasted Nuthatches aren’t known to share night-time sleeping quarters. A mated pair of White-breasted Nuthatches may share a roost hole, but I can’t find evidence of how often this happens.
Birds that don’t roost in cavities include large, well-insulated species like the bigger owls and hawks, and also many songbirds, from crows and ravens down to tiny Golden-crowned Kinglets. These birds tend to find fairly sheltered branches, usually close to the trunk, for sleeping. Some species share body warmth by huddling close to others, but most birds are surprisingly independent even when sleeping. They obviously can’t put on another sweater or another blanket—or can they? Every fall, northern birds grow a great many more body feathers—often as many as several hundred. We can’t see these insulating downy feathers beneath their outer contour feathers, but they contribute enormously to each bird’s ability to insulate itself against cold. When birds go to sleep, they erect their down feathers, which does the same thing as shaking out a sleeping bag or down comforter. And many birds can lower their thermostat at night, allowing their body temperature to drop dramatically to minimize the energy required to keep them alive. Chickadee body temperature can drop more than 20 degrees at nighttime. When birds awaken in the morning, they often shiver violently—the muscle activity quickly raises their body temperature so they can resume activity. It’s critical for birds, especially tiny ones, to feed frequently in winter, because the calories they burn are literally the fuel that keeps them alive. So feeding at first light is critical. Our feeder activity is highest in the first hour or two after dawn and again in late afternoon, when birds are stoking up for a long night’s sleep. Chickadees and nuthatches also cache food, and can raid their stores in the morning for a quick breakfast that gives them the energy to spend the rest of the day searching out new supplies and building up the store.
It’s hard to think about blizzards in October, whether we’re human or bird. But preparing for winter is part of what we do in autumn, just as pulling out garden catalogs is what we do in spring. And it’s good planning that keeps those chickadees not just thriving, but able to bring us good cheer on the coldest days.