The one characteristic that sets birds apart from other critters is their body covering of feathers. Many people might think that laying eggs would be another, but the fact is that many other creatures lay eggs. Insects, amphibians, reptiles, fishes and even some mammals lay eggs.
However, there is something else that is somewhat unique to our avian friends. To protect those eggs and future nestlings, most birds build some sort of nest or, at the very least, use the nests of other birds. Nests, and all the variability among the 9,648 species of birds, are nearly as fascinating as the birds themselves.
From the simple bowl-like depressions on the ground typical of killdeer to the complex weaved pouch-nests of Baltimore orioles, nests are most certainly worthy of our attention. In fact, becoming students of nests can help you become an even better birder. A lot of satisfaction can be derived from identifying the maker or owner of a nest based solely on the nest alone.
Ornithologists believe the risks of reproduction led to the diverse array of nests within the world of birds. After all, not only are the eggs vulnerable to predation by a host of predators, also at risk are the incubating adults and, later, the offspring and the parents caring for those offspring. Nests help reduce the dangers associated with predators and exposure to the elements as well as reducing the loss of heat during incubation.
While it's true that other animals build nests, birds do so on a much grander scale. From choice of sites, to construction materials, to the types and forms and more, bird nests are in a class of their own.
It's interesting to think about the different types of bird nests you may have encountered along the way. Many species of owls, for example, use the abandoned nests or tree cavities of hawks, eagles, crows, magpies, woodpeckers and other birds for their nests. They don't even build their own.
On the other hand, the nests of swallows reveal a great deal of variability and nest-type complexity. Cliff, cave and barn swallows are the only species of North American swallows that build nests of mud. And of these three, the colonial nesting cliff swallow builds the most complex mud structure.
Resembling a jug or gourd, the enclosed, one-entrance structure is typically built on rocks of cliffs, under bridges or the eaves of buildings. But other swallows, such as bank swallows, nest in burrows on exposed soil banks like those along rivers and some lakes. Simpler yet are the nesting habits of tree swallows and purple martins. Both species are cavity-nesters and will readily accept artificial birdhouses. Of the two, however, it is the purple martin that relies most heavily on human made nest boxes.
Nesting materials used to construct nests are wide-ranging amongst the many species of birds. And interestingly enough, of the 29 avian orders identified in the world, half are cavity nesters, which include kingfishers, woodpeckers and some owls, to name only a few.
Some birds, such as belted kingfishers, excavate cavities into the ground. Others, like woodpeckers, excavate holes into live or dead trees. Still other birds bore holes into only dead or rotting logs or trees. And then there are the many species of birds that rely on other species of birds, such as woodpeckers, to provide them a cavity to nest in. Chickadees and nuthatches are two resident species that utilize abandoned woodpecker holes for nesting and as shelter.
Materials used by birds to construct nests generally consists of plant materials such as grass, leaves, stems, lichens and twigs. Other materials include mud, rocks, snake skins, spider webs, feathers, hair and even human-made materials like ribbon, yarn, string and paper.
Some species of birds have figured out that the chemical properties of certain green plants help to combat parasitic infestations and disease. European starlings, for example, include yarrow or a species of nettle in their nests. The odor and the chemical compounds present within these plants apparently act to reduce bacterial growth and the hatching of insect eggs, like mites, that is so common inside the nests of birds.
Though nests serve to protect eggs and nestlings from predation, and indeed they do, an enormous number of nests are still found by predators -- this in spite of cryptic and inaccessible nests built by birds everywhere.
Several years ago, when I assisted with a waterfowl reproduction research study on the Great Plains of North Dakota, we discovered that nesting success was limited by not only the availability of suitable nesting habitat, but, most notably, by the abundance of predators. More than 80 percent of the hundreds of nests we located and monitored were depredated by predators such as skunks, fox, badgers, raccoons and even ground squirrels and gulls.
During the research, I was often delighted by what I encountered when monitoring a nest. I sometimes would have difficulty locating a duck nest that I knew was there because the hen and her natural camouflaged plumage made it almost impossible to detect her as she sat incubating her eggs.
Other times, however, it was when she wasn't there at all, because her eggs would always be carefully covered by fluffy down feathers that she had plucked from her breast in order to blanket the eggs and keep them warm while she briefly slipped away for a drink and to feed.
The nests of birds--whether the colonial ground nest of an American white pelican, a cavity nest of a bluebird, a weaver nest of the Baltimore oriole or a grass-lined cup-nest so typical of perching birds such as American robins -- are characteristically unique to each individual species of bird. Indeed, knowing what nest belongs to which bird is our trick to learn as we get out and enjoy the great outdoors.
BLANE KLEMEK is a Minnesota DNR wildlife manager. He can be reached at email@example.com.