Most birds go to great lengths to hide their nests. So when I find one, invariably so carefully crafted and astonishingly intricate, I’m filled with awe. They are marvels of the natural world.

The weave of twigs, grass, leaves and other natural materials is specific to each species. Most birds use nests only to raise their young. For small birds, this could be less than one month out of the year. For that reason, I generally don’t consider them homes. But the analogy is apt, if only to convey the uniqueness of their architecture. Of a house, you might say: That’s a craftsman or a Cape Cod or a colonial. The same sort of design distinction can be seen in a nest. That’s a robin’s nest or a warbler’s or a red-tailed hawk’s.

Birds can be choosy about the materials they use to build their nest. Some line their nests with snakeskin to ward off enemies. Others fasten lichens with spider silk to the exterior for camouflage. Still others stuff feathers inside dome-shaped nests of sticks or create false entrances to dupe predators or add aromatic leaves to repel parasites and enhance the immune systems of their nestlings.

Increasingly, and troublingly for what it says about the state of the planet, birds are also using all sorts of plastic litter and other trash to build their nests.

These photos reflect yet another way the human signature has affixed itself on the natural world. Among the trash that birds use to build their nests are strips of tarp; wrappers from gum, candy and cigarettes; plastic cotton and twine; shipping material; landscaping refuse; and insulation.