Where do birds go to sleep at night?
Many assume that songbirds retire to their nests during the dark hours, a natural assumption that seems to make sense, but is wide of the mark. The truth is that after they're finished raising their brood, birds say goodbye to their nests, abandoning the structures they worked so hard to build just weeks earlier.
For one thing, once young birds fledge, they leave a big mess behind, just like teenagers in the human world. A once-pristine nest now holds a layer of droppings, shed feathers, food bits and other debris. It may have attracted parasites like mites and is often in poor repair, after a lively brood has been bumping and jumping around in it for 10 days or more.
And adult birds know that their nearly constant coming and going to feed their youngsters may have caught the eye of a predator like a cat or carnivorous bird, just biding its time before making an attack. No, once nesting duties are completed, it's far safer to move away and leave the nest to the elements.
But birds remain in the area, since the factors that made a site seem safe for nesting also offer elements for a good night's sleep. Birds that nest in dense thickets, like cardinals and catbirds, move to a nearby shrub or vine at night. Goldfinches duck into an evergreen for nighttime shelter, as do blue jays and robins. Cavity nesters, like chickadees, nuthatches and woodpeckers, sleep in tree holes (or human-made nest boxes). And birds that nest on the ground, such as meadowlarks, white-throated sparrows and towhees, sleep on the ground, as well, in grassy tangles or piles of leaves.
Young birds will often sleep bunched up on a branch with their siblings for the first few weeks after fledging, the same kind of shoulder-to-shoulder contact they shared in their nest.
Consider a backyard landscape, with cardinals sleeping in the shrubbery, catbirds bedding down in the grapevine, house finches nestled in the Virginia creeper climbing the house, a downy woodpecker dozing in a tree hole and a chickadee sleeping in the nest box. Another question then arises: How do the cardinals, finches and catbirds keep from falling off their perches when they're fast asleep?
Birds have a foolproof system to stay anchored to their perches, since falling-while-groggy could be very dangerous if a cat or other scavenger were around. After landing on a branch to spend the night, birds bend their legs, causing tendons in the feet to lock tightly. They remain this way until standing up in the morning, which causes tendons to release.
How deeply do birds sleep? Frankly, birds live dangerous lives, and they must be alert for predators at all times. Many species have the ability to sleep with one eye open and half the brain awake, called unihemispheric slow-wave sleep, a fascinating process still being studied. These birds can switch between brain hemispheres to rest one half at a time — but if they feel safe and protected they can put both sides of the brain to sleep. (Migration and nesting season create major sleep deficits but birds rest up with frequent "cat naps.")
Not that much is known about the sleeping life of birds, since they're very stealthy when approaching their sleeping quarters, and are difficult to study in the dark. If you find an abandoned bird's nest, you can be fairly certain that birds are not using it at night, although sometimes a savvy mouse will move in for the winter.
St. Paul resident Val Cunningham, who volunteers with the St. Paul Audubon Society and writes about nature for local, regional and national newspapers and magazines, can be reached at valwrites@comcast.net.
Help birds catch 40 winks
Maintain sheltered places, such as brush piles, evergreens and roost boxes.
Clean out nest boxes after nesting season for cavity nesters to doze in.
Discourage prowling cats and add predator guards to nest boxes and roost boxes.
Turn off outdoor lights that can disrupt birds' sleep and attract predators.