By Laura & Hal Mahan
One of our favorite stories is about a group of zoology graduate students studying birds who were lamenting the fact that “everything is already known” and there was nothing left to discover. Their astute professor seized this teachable moment and assigned this task. He brought into the lab the nest of an American Robin and took the nest apart, separating the component parts onto the lab table. He then assigned this task: using only tweezers to simulate a Robin’s beak, put the nest back together again. Of course, the students failed the assignment!
March is the beginning of nesting time for our songbirds. They are the builders of the natural world. Just as humans build homes out of bricks or wood, held together with mortar and nails, birds build nests of natural materials held together in various ways and then lined with finer, soft materials making a plush carpet of protection for the eggs.
Bird nesting strategies are varied and fascinating. Some birds take the easy way out and simply form a depression on the ground, scraping away rocks and sticks, and laying eggs without other adornments to the nest. These birds, such as the Killdeer (a type of shorebird), generally have young that hatch fully formed and ready to leave the exposed nest.
It makes sense that some birds have taken to the trees for nesting, making it more difficult for predators to reach them. Generally, the birds that nest in trees have young that hatch in a helpless state, requiring some period of constant feeding and attention from one or both parents. The types of construction materials they use depend on the size of the bird and the resources available. Some larger birds, such as hawks, carry sticks up into a tree and build a simple platform nest. Small birds such as warblers and vireos weave finely constructed baskets, held together with sticky things like spider webs, wet moss and wet leaves. Catbirds and Brown Thrashers line their nests with wet rootlets from plants. These rootlets are moist and flexible when placed in the nest, but then dry and become like small wire springs to serve as the inner bracings to hold the nest in shape and provide more protection for the young. Apparently, birds have become masterful at determining the physical properties of their nesting materials, using for example more bracing material when the nest is in a windy spot, or more mud to hold together a nest of particularly short pieces of twigs.
Relatively few species of birds nest in cavities in trees, and these are the birds that we can help by providing suitable nest boxes or bird houses. Their natural nesting situations have declined dramatically as we remove dead trees from our yards and woodlots. You can encourage birds such as screech owls, woodpeckers, bluebirds, nuthatches and chickadees by putting out nest boxes in the appropriate locations with the right-sized entry hole.
For Further Investigation
Nests, Eggs, and Nestlings of North American Birds by Paul J. Baicich & Colin J. O. Harrison
Peterson Field Guide: Eastern Birds’ Nests by Hal H. Harrison
Laura and Hal Mahan are owners of The Compleat Naturalist, located at 2 Brook Street in the Historic Biltmore Village. To learn more, visit CompleatNaturalist.com or call 828.274.5430.