Annual Construction of “Home”
By Noreen O’Brien, Purchasing, Marine Parts Express
Imagine having to build a new house every year. Egads. I struggle with the very idea of a move, much less the need to construct a home first—and then on an annual basis. Most birds from hummingbirds to eagles build or reconstruct nests that take all forms, from a simple scrape in the ground to an elaborate construction. That’s a lot of expended energy, but it must be worth it for them to do it year after year.
Birds have the most highly evolved nests known among nest builders; however, not all birds build nests and not all nests are complex. How the young are born determines the complexity of any given species’ nest. Some birds, like Killdeer, are born precocial—when they hatch, they can walk within the first 24 hours, they have down in advance of fully formed feathers, and their eyes are open. Most chicks, such as those of songbirds, are altricial—helpless, unable to stand, they have closed eyes and nearly no feathers. These hatchlings are totally dependent on their parents for survival for days, weeks, or sometimes months. The parents of altricial chicks build the best nests, for obvious reasons.
The home habitat must offer protection from predators, have nest-building materials, and a food source to raise the young. Most songbirds nest in vegetation, some in natural cavities, while others build a nest tucked away in a tree or a bush. American Goldfinches, whose nesting time appears to be correlated with maturing thistle and other seeds used as down for nest building and as food for the nestlings, build their cup-shaped nests in late summer in a fork of a horizontal tree limb up to 30 feet above the ground.
Killdeer, a shorebird, makes a simple shallow scrape on gravelly ground or a flat rooftop, sometimes at quite a distance from water. These nesting sites are almost impossible to see, even when the bird is sitting on the speckled eggs that blend perfectly with the surrounding gravel. However, this location offers the incubating bird an extended view of the surroundings and a chance at escape should a predator approach.
Get too close to a Killdeer nest and the incubating parent first runs a short distance, and then lifts high into the air screaming, “kadee, kadee, kadee.” Approach the nest, even unintentionally, and a parent bird drops to the ground, again calling loudly bringing attention to its apparent vulnerability as it feigns a broken wing to distract attention from the nest or the chicks. Their camouflaged chicks, little balls of fluff running around on stick legs, become visible only as a flash of movement.
Bald Eagles prefer to lay their two or three eggs in a nest of an immense pile of large sticks and branches lined with grass, moss, and sod near the crown of a large tree, away from predators and other eagles, and near water, their food source. These birds repair and enlarge the nest each year, making them the largest nest of any North American bird. According to the Department of Wildlife (Oklahoma) Web site, the “record nest measured 20 feet deep, 10 feet wide and weighed two tons.” Eagle nests eventually topple from their own weight. Perhaps this is the reason this species sometimes has a second nest for use in alternate years.
While most birds nest as an individual pair, some are colonial. Great Blue Herons build their large, messy stick nests with other Great Blues. Sometimes, several nests in a single tall tree in remote, inaccessible areas near shallow water. At a rookery I used to visit in Massachusetts, it was a most impressive sight to view these giant birds totaling about 100 adults, each pair feeding an average of about four young on some 50 nests. More impressive was witnessing the herons manipulating the large sticks into a form that would keep the eggs from falling through the floor of the nests.
Then, some birds, like the Brown-headed Cowbird, don’t build a nest at all. In fact, this species doesn’t even raise its own offspring. Instead, the cowbirds lay their eggs in the nest of other, unsuspecting birds and abandon them for the foster parents to brood and raise—sometimes at the expense of the host’s own young.
There are almost as many kinds of nests are there are birds, but each species follows the same essential nest plan from generation to generation. Next time you find a nest (don’t remove the nest, because that’s illegal), examine the habitat, take copious notes on the materials used, style of construction, and the location, perhaps take lots of photos, and then attempt to determine the builder of the structure. You may want to pick up a copy of A Field Guide to Birds’ Nests by Hal H. Harrison to help you along the way.
And remember to appreciate that you don’t have to build your home annually.
Meanwhile, to see a live Webcam of a pair of Bald Eagles and three eaglets on a nest in Iowa, go to http://www.huffingtonpost.com/2011/04/06/eagle-cam-decorah-iowa_n_845635.html.
Alternatively, a pair of Ospreys are refurbishing a nest that may be viewed through a live Webcam out of the Taste of Maine Restaurant in Woolwich, Maine, at http://www.briloon.org/watching-wildlife/osprey-cam.php. The Ospreys have only just arrived, so there are no eggs yet. Keep watching and you will be able to see the chicks hatch and evolve into fledglings.
Or, go to http://watch.birds.cornell.edu/nestcams/home/index to see what other options are available for Webcam viewing.
Till next …
We at Marine Parts Express find this talk of nests a bit disturbing and eyrie. Still, just like the mother birds take care of their young (with the exception of that profligate cowbird), Marine Parts Express takes care of its customers. Call us toll free at 877.621.2628.
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April 14, 2011 / Noreen O'Brien / 0
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