Winter Nights Challenge Birds’ Survival
by Val Cunningham
Nighttime Sleeping Spots
One mid-winter day I looked out an upstairs window late in the afternoon just as a chickadee flew to the backyard’s tall silver maple. He loudly chattered his “chick-a-dee” call several times, and then disappeared into a hole created when a branch fell in an ice storm. This, it turned out, was the little bird’s nighttime sleeping spot.
The next day at dusk the chickadee flew in, looked around, made his parting announcements, then hopped into his cavity. It became my habit to look for him just before dark, and he never disappointed: a quick flight, a few vocalizations and then he’d disappear. As winter advanced and the days lengthened, he continued to arrive just at dusk, thus a little bit later each day. I could have set a clock by him, if I had one that ran on circadian time.
The chickadee’s behavior illustrates how birds don’t need watches to know what time it is, with many of their internal rhythms keyed to the sun. But it also points up another phenomenon: in order to survive on winter nights, birds need protective shelter, and for this they tend to seek out habitat similar to summer nesting sites. For some that means a tree hole, for others it means tucking away in thick shrubbery.
Since chickadees are cavity nesters it’s natural for them to search out a tree hole or nest box to roost in at night. These offer shelter from wind and snow and safety from most predators.
Some birds, notably bluebirds, will bunch up inside cavities on very cold nights, sharing their body heat with others of their kind. Those bluebirds that remain in our area all winter often sleep in nest boxes where they raised families last summer.
Woodpeckers sleep alone but are cozy at night, too, after busily spending fall days excavating holes in trees, utility poles and, sometimes, people’s houses. Many woodpeckers will chisel out more than one hole, because they’ve learned how valuable this real estate is. Red, gray and flying squirrels often commandeer woodpecker cavities for their own nighttime comfort.
Nuthatches will sleep in old woodpecker holes (but they won’t evict an occupant) and screech owls like to roost during the day in tree cavities and wood duck boxes.
Other birds, like cardinals, blue jays and house finches, all “outside nesters,” head for the densest vegetation they can find, whether a stand of now-leafless shrubs, a tangle of vines or evergreen trees or shrubs. I’ve observed a pair of cardinals darting into an arborvitae shrub near our back door just before dark. Evergreens offer some of the best protection from wind and cold, and backyards with conifers are among the most bird friendly.
Why don’t outside nesting songbirds use their summertime nests as shelter? These often are now falling apart after summer’s hard use, and autumn’s leaf drop may leave them exposed to the elements.
Some birds use snow’s insulating qualities to their advantage. For example, ruffed grouse are known to dive into deep snow to create a nighttime snow cave.
None of these tactics—sleeping in tree holes, roosting in groups, huddling inside dense shrubbery—is foolproof. When nighttime temperatures drop far below zero for extended periods, some birds will freeze. The hardiest survive the best, and those that can face a long winter night with a full belly are more likely to wake up in the morning. Our backyard feeders can provide a real boost to birds eager for a meal as the light fades.
St. Paul, Minnesota resident Val Cunningham, leads bird hikes for the St. Paul Audubon Society and writes about nature for local, regional and national newspapers and magazines.