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Nests Come in All Shapes and Sizes

July 01, 2009 - A characteristic feature of all bird species is a nest in which eggs are laid. Nests range from small depressions in the forest floor to massive structures weighing more than a ton.

The simplest nests are mere scrapes on the forest floor, fields or beaches. The nest of a killdeer is a good local example. The female lays four eggs in a nest scrape just big enough to contain the eggs. As you would expect, the eggs are well camouflaged. In the woods, American woodcocks and whippoorwills create nest scrapes for their eggs.

For most species that create nest scrapes, little effort is made to line the nests with soft material. Birds that make nest scrapes spend very little energy in making a place to lay eggs and raise their young.

Most birds construct a bowl-shaped nest just large enough to fit an adult's body. Let's use an American robin nest as a typical example of a bowl-shaped nest.

Robins are not great architects, but still have a remarkably complex nest. The outer part of the nest is formed of twigs, coarse grass and sometimes pieces of cloth, string or other human-made products. This outer layer gives the nest strength. Within this outer layer, robins place a smooth layer of mud.

Finally, a layer of fine grasses is laid down to surround the eggs and aid in insulation. Once the outer part of the nest is built, the female sits in the middle of the nest for the rest of the construction. A snug fit is therefore guaranteed for the incubating mother. The nest is usually in a tree from 3 feet to 25 feet high.

Other species use specific materials for the inner lining of their nests. Palm warblers, a ground-nesting species in bogs, often place ruffed grouse feathers in their nests. Tree swallows line their nests with feathers, particularly white ones.

Ruby-throated hummingbirds create tiny nests to hold their two eggs. The nest is made of down and small pieces of plant material bound together with spider webs. The outer part of the bowl is covered with bits of lichens to aid camouflage.

Black-capped chickadees make their nests in tree cavities. The outer part of the nest is made of moss and the inner part of spider webs, soft grasses and plant down.

Water birds typically create bowl-shaped nests on the margins of lakes or ponds or even on floating vegetation. In most cases, the outer layer of the nest is made primarily of vegetation. If water levels rise, water birds will quickly add additional vegetation to keep the inner part of the nest dry.

The inner lining is made in part of down feathers that the female pulls from her breast. These down feathers create a wonderfully warm place for the eggs. You take advantage of the excellent insulating qualities of duck down if you own a down coat or sleeping bag.

The largest nests in Maine are made by birds of prey. An osprey nest may be 5 feet across. The outer portion is made of sticks and miscellaneous debris. The inner lining is made of smaller twigs, grasses and other soft material. Both the male and female participate in nest building. The male tends to bring material to the nest site and the female incorporates the material into the nest.

Bald eagles make Maine's biggest nests. Some eagle nests may be 8 feet in diameter and 12 feet high. The weight may exceed one ton.

Like ospreys, bald eagles use the same nests year after year, adding material to the nest each spring. Great horned owls will readily adopt an abandoned osprey or eagle nest.

Some of our birds place domes over their nests. Such nests are characteristic of many of our wrens.

The family name for the wrens, the Troglodytidae, comes from the Greek for "cave-dweller," reflecting the shape of the nest. One of our most common warblers, the ovenbird, builds a domed nest on the forest floor. The shape of the nest suggests a Dutch oven.

Distinctive nests are made by Baltimore orioles. Their nests are made of grasses, vines and hair. The nest is a deep pouch, bound to the forks of a branch at the rim. Two sprites of the Maine woods, the ruby-crowned kinglet and golden-crowned kinglet, also create hanging nests that are much smaller and more difficult to see than oriole nests.

HERB WILSON / BIRDING, Portland Press Herald, June 28, 2009


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