The nesting season continues apace for many Maine breeding birds. Finding a bird’s nest can be difficult during the incubation period when the incubating parents are still and rarely leave the nest. For songbirds and other birds whose young require feeding (altricial birds), the necessity of frequent visits to the nest to satisfy the seemingly insatiable appetites of the nestlings makes it easier to locate nests after the chicks have hatched.
Birds of a given species make similar nests. Nests range from small depressions in the forest floor or on a sandy beach to massive structures weighing more than a ton. In today’s column, I will provide an overview of the diversity of bird nests.
The simplest nests are 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 Whip-poor-wills create nest scrapes for their eggs. For most species that create nest scrapes, little effort is made to line the nests with soft material.
Most birds construct a bowl-shaped nest just large enough to fit an adult’s body. We can consider the bowl-shaped nest of an American Robin as a typical 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.
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. In the early breeding season, you can see aerial fights where Tree Swallows attempt to take white feathers from another Tree Swallow.
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 a tree cavity. The outer part of the nest is made of moss and the inner part of spider webs, soft grasses and plant down.
Waterbirds 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, waterbirds 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.
The largest nests in Maine are made by birds of prey. An Osprey nest may be five 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.
Bald Eagle nests are larger yet. Some nests may be eight feet in diameter and 12 feet high, weighting over a ton! Like Ospreys, Bald Eagles use the same nests year after year, adding material to the nest each spring.
A good source for identifying nests based on their structure and location is http://nestwatch.org/learn/how-to-nestwatch/identifying-nests-and-eggs/