In winter we find more birds’ nests than at any other season. It’s not that we aren’t looking the rest of the year; it’s just that the leaves get in the way. But after autumn comes and goes, the bare limbs of trees are decorated by the deserted homes of our avian friends.
An expert can identify a species of bird by its nest, for each robin and wren follows its own species’ master plan. But not all birds construct an actual nest.
The simplest nest we’ve found was that of a killdeer in North Carolina. We drove into an overflow parking lot and noticed the bird standing surprisingly close to our motorhome. As we got out and walked closer, the killdeer put on the “broken wing” display typical of the species. She tried her best to draw us away from what we now knew must be a nesting site, but there was nothing in the area but golf-ball-sized gravel covering the field.
A careful search turned up the nest - a slight depression in the gravel, filled with four eggs that perfectly matched their surroundings. We drove around the “nest” on our way out, hoping that the eggs would soon hatch. It was nearly summer, and time for that parking lot to get heavy use.
At the other extreme are the birds that construct elaborate nests. The oriole hangs its bag-like nest from the tip of a branch. The finished product is a masterpiece of weaving and is easily identifiable from a distance.
Some birds, such as the woodpeckers, may spend months constructing a nest. Their hammering often starts as early as January, with breeding not begun until April. But even among woodpeckers there are noticeable differences among the nests of various species. A bird such as the hairy woodpecker may choose a live aspen or oak tree for its nesting hole, while the weaker-billed flicker must seek a dead tree.
Woodpecker holes aren’t just for woodpeckers, either. Many cavity nesting birds aren’t capable of chiseling their own holes, so they use old woodpecker nests. Bluebirds are notable examples, but so are house sparrows, small owls, and some flycatchers.
There’s another bird that uses the nests of others, but it doesn’t wait until the following year. The cowbird lays its eggs in the nests of other species, and lets somebody else hatch and raise the young. Because the baby cowbird is often larger than the chicks of its foster parent, the young cowbird is sometimes the only survivor at the end of the nesting season.
Nests come in all sizes, with the smallest being built by the rubythroated hummingbird. It is only one inch deep and one inch across, and the hummingbird incubates eggs with her head sticking out one end and her tail out the other.
At the opposite extreme is the nest of the bald eagle. In Ohio one that was estimated to weigh two tons finally tumbled to the ground. In Florida another was measured as being 9 1/2 feet across and 20 feet deep.
An eagle’s nest is reused year after year, so it just keeps getting larger. But most smaller birds build a new nest each season. Some, such as the robin, build as many as three nests per year - one for each of their three broods.
The amount of effort expended in nest building can be observed by watching a barn swallow construct its nest. In making its nest made of mud plastered to a wall, the typical swallow makes in excess of 1,200 separate trips carrying building material.
Once you start looking for bird nests you’ll discover them in some strange places. Like the tree swallows that decided a good place for a nest was on a ferry boat. It didn’t seem to matter to the parents that their nesting site was constantly changing location. They still successfully raised their young to maturity.
You’ll also find nests built from strange materials. Birds may be programmed to construct a certain type of nest, but if the proper materials aren’t easily available, the birds improvise.
Many birds use molted snakeskin in their nests, but if the snakes don’t cooperate, they may substitute manmade material such as cellophane. Or if a bird that uses animal hair can’t find any lying around loose, it may pluck some from the nearest live animal - possibly a human.
Sometimes a bird finds a substitute material that’s easier to work with. For example, there’s the vireo who built a nest entirely of Kleenex. And someone once found a brown thrasher’s nest that included a five-dollar bill.
Nest building is not just instinctive among birds, their very nature compels them to build. The nesting urge was so strong in a raven that when it couldn’t find suitable material it built a nest entirely of barbed wire.
But the most interesting nest we’ve ever read about appeared in California. A kleptomaniac wren built its nest near an office building. For materials it used only office supplies - rubber bands, thumbtacks, safety pins, paper clips, and whatever else it could find lying around. This tiny bird’s nest contained a total of 1,791 items and weighed 2 1/2 pounds.
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