A robin flies into a Morning Sentinel newspaper tube to sit on a nest with four eggs in Skowhegan. David Leaming/Morning Sentinel

Now is a great time to find nests. Many songbirds are feeding their ravenous young with the high metabolism of the quickly growing nestlings requiring frequent parental trips to and from the nest. A little patient observation will allow you to find it.

Since most birds do not re-use a nest from year to year, you can remember where a particular nest was and take a close look at it in the fall after the nesting season is done.

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.

The palm warbler will often use ruffed grouse feathers to help build its nest. Andy Molloy/Kennebec Journal

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 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.

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.

One American bald eagle sits in a nest with eggs as another readies to take off from a tree overlooking the Messalonskee Stream in Waterville. Eagles build the biggest nests you will find in Maine. David Leaming/Morning Sentinel Sentinel

The largest nests in Maine are made by birds of prey. An osprey nest may be five feet across with the outer portion made of sticks and miscellaneous debris and the inner lining made of smaller twigs, grasses and other soft material. Bald eagle nests are larger yet. Some may be eight feet in diameter and 12 feet high, weighing over a ton.  Like ospreys, bald eagles use the same nests year after year, adding material to the nest each spring.

Finally, some of our nesting birds build their nests in cavities. Woodpeckers excavate their own cavities while others rely on natural cavities or abandoned woodpecker cavities. The list of native cavity-nesting birds is diverse, including wood ducks, hooded mergansers, great crested flycatchers, tree swallows, black-capped chickadees, tufted titmice, house wrens and eastern bluebirds. For chickadees, the outer part of the nest is made of moss and the inner part of spider webs, soft grasses and plant down.

Two introduced species – European starlings and house sparrows – nest in cavities as well. These two species compete with native birds for available cavities. House sparrows will kill nestlings of other species and take over the nest cavity. I am certainly not alone in having a clutch of eastern bluebirds lost to house sparrows.

A good source for identifying nests based on their structure and location is nestwatch.org/learn/focal-species/

Herb Wilson taught ornithology and other biology courses at Colby College. He welcomes reader comments and questions at whwilson@colby.edu