Masters of Construction: Bird Nests

 

Likely pine warbler nest.

Likely pine warbler nest.

Consider this: the average human brain weighs roughly 1300 grams (2.86 pounds). A warbler brain weighs about 513 mg. (.00113 pounds). But while a human must spend untold hours and tens of thousands of dollars in order to learn to build a house, the warbler does so as a natural part of its growth process, and in response Spring’s most basic instinct: the urge to procreate. Granted, the plan does not always go as expected, and humans sometimes find themselves scratching their heads at the choices of location, materials, or design. Yet when it comes to building something from nothing, a shelter that is absolutely necessary for the survival of its young, birds have humans beaten, wings down.

Take the racquetball-sized example that fell from a tree a few weeks ago. The walls are constructed from strips of bark, going from pieces the thickness of shirt cardboard on the interior walls to paper thin on the outside, woven together by some level of engineering beyond the ken of the average human. The interior is lined with pine needles, which are both flexible and strong, and would have held the eggs in place well. Despite its magnificent construction, the high winds of an unseasonable April succeeded in scooping it from its place in the branches of a pine tree and tossing it carelessly to the ground. While identifying the owner of any nest is often difficult without actually seeing an adult nearby, a birder friend made the guess, based on timing of the build and its proximity to pine trees, that it belonged to a pine warbler. It is also the earliest nest builder among the many species of warbler.

DSC08108
On the other end of the local spectrum is the nest of the osprey. Unlike smaller birds, the ospreys not only mate for life, but they usually return to the same nest year after year. Their first nests may be a modest three feet in diameter. When they arrive in Rhode Island in late March, the first order of business is home construction and repairs. Particularly in the early season, these raptors with their nearly six-foot wingspan carry sticks, reeds, and dried seaweed to their nests atop tall trees or manmade platforms. If the nests aren’t destroyed within the first few seasons, it will continue to expand ultimately growing to eight feet across and six feet deep, fully exposed to wind and rain. The nest’s high position affords the chicks protection from land based predators, while the adults have the space to take off and land, all the while enjoying an unobstructed view of their watery territory.

Of course, not all nest locations make quite as much sense. While the pine warbler lost its hard work to the wind, it usually builds safe within the branches of a – you guessed it – pine tree. The pine warbler is rarely found anywhere other than in pines, since these trees provide both nesting sites and food sources from the seeds of the pine cone. However, there are often nesting choices that make no sense to the human mind, and often provoke questions regarding the feathered individual’s sanity.
The killdeer is certainly an example. This is an inland version of the piping plover. And like the piping plover, its nest is built mainly from…well, nothing. When the bird is in courtship mode, it tempts the female by making tentative nests, called scrapes. These are as simple as depressions in the dirt, grass or sand made when the male shakes his breast feathers on the ground to outline the location for a nest. If the lure is successful, the eggs may later be laid in that tiny divot “au naturel”. Only afterward will the killdeer attempt the most minimal of nest building, sometimes by gathering a few pebbles, or perhaps never adding any materials at all. Hardly the engineering miracle of the warbler.

The killdeer, winner of the award for worst nest location.

The killdeer, winner of the award for worst nest location.

Then, to borrow a real estate term, there’s the issue of location, location, location. Realtors list those “three” factors as most important in the successful sale of a home, and the siting of many bird nests reflects a similar value on location. Not for the killdeer, though. Perhaps the only thing that matches the killdeer’s disregard for form in nest building is its similarly carefree attitude toward location. Killdeer will nest on lawns, parking lots, driveways; pretty much any flat, open area. The bird in these pictures chose a location on the grounds of a high school, busy with foot traffic, lawn mowers, team practices. A veritable highway of activity. It is nearly impossible to believe that the population is robust enough to be considered a species of least concern by scientists.

Four eggs in the nearly non-existent nest of the killdeer.

Four eggs in the nearly non-existent nest of the killdeer.

Despite the more questionable choices birds make in choosing a nesting site, the fact remains that, here in Rhode Island at least, most species of birds that nest here will be successful. Whether hidden deep in a pine tree, high atop an open platform, or smack in the middle of a high school yard, the ingenious creations of birds will house the next generation. Not bad for a bird of very little brain.

 

 

(Update: Groundskeepers at the high school agreed to leave the area undisturbed once informed about the nest location. Good news. However, a day after this story was written, students accidentally destroyed the nest. An adult who knew the nest was there allowed them to play football in the area. One more example of the threats birds face when trying to raise a brood.)

Leave a comment