Don Lyman
The Boston Globe, April 22, 2022
A robin feeds her young in the nest. BILL BYRNE/MASSWILDLIFE
On a cold, damp March morning, I heard a crow calling loudly from high up in the bare branches of a maple tree. I watched as the large, black bird used its bill to break off a foot-long twig, which it carried to the crown of a nearby white pine where it was likely constructing a nest.
Spring is nesting season for most birds in Massachusetts, and many of our avian neighbors are busy building structures where they can incubate their eggs and raise their young.
Some birds in our area, such as great horned owls, nest in late winter, while others, such as blue jays, tree swallows, and wrens, wait until April, according to Wayne Petersen, Mass Audubon’s director of the Massachusetts Important Bird Areas program. Neotropical migrants such as warblers and orioles don’t arrive and start nesting until May. Others, such as goldfinches and cedar waxwings, wait until later in the summer to breed.
“Late May and June are peak times for nesting,” said Petersen.
Diet is a principal factor for when birds breed, explained Petersen. They need to make sure food is sufficiently available for themselves and their hatchlings.
“For example, cuckoos nest late [usually late May to early July] because they’re caterpillar eaters, so they need to wait for caterpillars to appear,” said Petersen. “And goldfinches feed primarily on thistle seeds, so they breed in August when pink thistles set seed.”
But climate change could alter nesting cycles, Petersen explained, if insects start emerging early because of an earlier spring, and neotropical migrants get out of sync with the insects and caterpillars they feed on.
A young ruby-throated hummingbird in a nest getting ready for its first flight. Hummingbirds often use lichens and spiderwebs in constructing their nests. CRAIG GIBSON
From 2-inch-wide hummingbird nests to 5-foot-wide eagle nests weighing hundreds of pounds, bird nests vary in size, structure, and materials used to build them.
Peregrine falcons often nest on rocky ledges where they make a simple scrape to create a depression in the sand or gravel substrate, according to the Cornell Lab of Ornithology website. Other birds, like wild turkeys and shorebirds such as plovers and sandpipers, do essentially the same thing in their nesting areas, Petersen said.
Ducks pluck their own feathers to line a nest that looks like a feathered cup on the ground, said Petersen. Kingfishers will excavate holes in riverbanks to nest in, as will bank swallows, which nest in colonies in places like gravel pits and riverbanks. Some sea birds, like terns, nest in colonies as well. Woodpeckers drill holes in dead trees for nests. These holes are also utilized for nesting sites by other bird species, like screech-owls.
Cliff swallows, which nest on cliff faces and under bridges, make their nests out of mud, said Petersen. The finished product looks like a bowl with a hole in it. The Cornell Lab said each cliff swallow nest is composed of about 1,000 individual mud pellets.
The bird nests most people are familiar with are constructed in trees and shrubs.
Some, like mourning dove nests, are little more than a pile of twigs and grass stems, while others, like crow nests, are a bit more complex, and in addition to sticks include an inner cup lined with pine needles, weeds, and soft bark, according to the Cornell Lab website.
Many birds build fairly intricate nests, said Petersen, weaving grass and twigs together to form a basket-like structure. Baltimore orioles weave elongated nests from plant fibers that are so tightly woven together they’re hard to pull apart.
Hummingbirds and blue-gray gnatcatchers use spiderwebs to bind their nesting materials, while robins build heavy bowl-shaped nests made of plant materials plastered with mud.
Some birds, like tufted titmice, will steal hair from animals like foxes and raccoons ─ a phenomenon called kleptotrichy ─ to use in their nests.
Birds will also utilize manmade materials for nest building. Petersen said he has seen rope, netting, fishing floats, and even deflated Mylar balloons in osprey nests. Orioles will use colored pieces of yarn. Petersen said he saw a photo of a brown thrasher’s nest with a five-dollar bill placed at the nest’s bottom.
How do birds know how to build nests? Chris Milensky, a museum specialist in the Division of Birds at the Smithsonian National Museum of Natural History, said in an article that scientists believe nest-building is primarily instinctive, but it has been shown that there is a learning component, and birds that build intricate nests become better at it over time.
In many bird species, the males collect the nesting materials, but the female does most of the construction, Petersen said.
“Males establish the territory,” said Petersen. “Females do most of the incubation, and females decide where to put the nest within the territory.”
Most birds build new nests every year, but some large raptors, like ospreys and eagles, will reuse nests and just clean them up a bit, adding new materials as needed, said Petersen. Sometimes they’ll even add a few sprigs of evergreens, like pine or hemlock, perhaps as a sign that the nest is occupied.
Some birds, like great horned owls, don’t make their own nests, but rather, use empty red-tailed hawk or great blue heron nests, Petersen said.
Brood parasites, like brown-headed cowbirds, actually lay their eggs in the nests of other bird species, such as warblers, in an effort to trick the nest owners into raising their chicks, Petersen said.
Some birds nest in unusual places. For example, Petersen said he’s often found brown creeper nests under loose pieces of tree bark.
Petersen said house sparrows sometimes nest in the sides of osprey nests, where perhaps the large raptors inadvertently provide protection from predators.
Although robins usually nest in trees, Petersen said he’s heard of robins occasionally nesting on ferry boats, where they come and go with the ferry, or wait until it comes back to attend to their offspring.
Phoebes, common songbirds in suburban neighborhoods, often nest on porch lights or other parts of peoples’ houses, said Petersen, and small birds like house sparrows and wrens will sometimes nest in wreaths, baskets, and flowerpots.
Chimney swifts nest in chimneys and use their own saliva to paste sticks to the inside, said Petersen.
“Birds are very good at concealing nests,” said Petersen. “There’s almost no limit to what birds will do with nesting.”
A juvenile bald eagle above the nest. BILL BYRNE/MASSWILDLIFE
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