Nature Notes: The Nesting Instinct

    Just about every local bird that is going to nest on Long Island is already nesting. Some early birds such as the great horned owl, Canada goose, and mallard have almost finished, in other words, the young have left the nest. Because every species is different, every nest is different in some aspect, although they share a few traits in common. They’re round, who ever heard of a square nest? The nest centers are composed of softer materials than the outer parts to keep the babies cozy. The outsides are for durability and protection.
    Many birds are hole nesters, but most build conventional nests. Several species nest on the ground, but most nest off the ground. Obviously, ground nests are vulnerable to a host of mammals including foxes, feral cats, raccoons, opossums, and rats, as well as snakes and even turtles. But what they offer in exposure, they make up for in protection from winds and storms, which can shake nests or their chicks out of a tree.
    Terry Sullivan was watching a male Baltimore oriole peel 12-inch-long strips of mallow bark from about five old mallow stems in his yard. The orioles make that unique hanging nest that sways in the wind without falling down. This one was using the mallow peels to make the tough structures that go over the limb to attach to either side of the nest, keeping the nest from blowing away. Thus an oriole nest can hang far out from the tree’s center, while conventional nests have to be anchored to a crotch closer in.
    The simplest nests of all are the ones made by piping plovers: a few fragments of shell in a depression on the upper beach. Piping plover chicks are precocial — as soon as they hatch out, they are up and running around. A more elaborate nest against a backdrop of white sand would be easy for predators to spot from the air.
    Some birds use the nests of others. The female brown-headed cowbird is notorious for laying her eggs in an active nest of another species. Her young most often win out in the competition that ensues. Great-horned owls use last year’s red-tailed hawk nests for starters. Well-established osprey nests are not only used by an osprey pair, but often by house sparrows and a few other small songbird species that nest in the fringes without much worrying from the original nest owners.
    Most songbirds are solitary nesters. A nesting pair has a territory that they defend against other members of the same species. Mockingbirds are more aggressive; they try to kick out all the species from their territory including some four-legged and bipedal ones.

    Then, there are the colonial nesters like the cormorants, terns, and gulls. There is strength in numbers. Anyone who has entered a least-tern nesting area knows that.
    I remember being taken aside by Lee Radziwell in the early 1990s and asked rather pointedly, “Can’t you move those nests to a spot down the beach away from houses?” She was tired of being attacked by the terns, as were her dogs, every time she tried to walk down to the water from her house near Wiborg Beach in East Hampton Village.
    Some cavity-nesting birds have given up making nests altogether. If it weren’t for birdhouses in which to incubate and raise their young, one wonders if they would breed at all. Purple martins may still breed in holes in the wild but the large majority of them breed in martin houses or arrays of hollowed out gourds. Yes, a pair of ospreys builds and rebuild the same nest year after year, but what would happen if all of the manmade and man-erected osprey platforms blew over in a storm and weren’t replaced. There would be pandemonium. Would the ospreys give up, or would they think back to the time they nested in trees and begin that cycle anew?
    Just like some humans, some bird species are not that democratic. The house wren is one of those. It will stuff every nesting box or tree hole in sight in a given area but only use one of them for its nest. It completely eliminates the competition that way. Greedy little fella.
    Some birds are poor builders. The mourning dove’s nest is no work of art and frequently has spaces big enough for an egg to fall through. There is a tern in the tropics of the Old World that doesn’t build a nest, but is content to lay an egg out in the open in a nook on a tree branch. Take the peregrine falcon. It is just as content to nest on some high concrete ledge of a New York City skyscraper as on some aerie on the rim of a dormant volcano. To the peregrine, the big building is nothing more than just another mountain peak standing among dozens of others.
    On the other hand, if all birds nested in the same way and all nests were generic, wouldn’t it be a dull world?