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.
Distressing as this may be, it’s also a sign of ingenuity. Birds, which evolved from small carnivorous dinosaurs some 150 million years ago, are adjusting to the human-dominated world they inhabit. Studies of this behavior suggest that it is now widespread.
Do these materials attract unwanted attention from predators? Or entangle nestlings? We don’t fully know what impact all this trash is having on birds. There may be benefits to some of the rubbish they add. Plastics may strengthen nests. Polyester wadding may better insulate nests than natural materials, helping nestlings maintain optimal body temperature. The nicotine and other compounds in cigarette butts incorporated into nests may repel parasites. On the other hand, nestlings may eat some of the plastic or other trash, resulting in sickness or even death.
There is, nonetheless, a beauty and resilience to these creations. It’s amazing that birds recognize and match the properties of plastic and other trash materials to natural ones. I’ve seen shreds of tarp replace grass to suspend nests from branches and plastic cotton used instead of plant fibers to insulate eggs.
Yes, it is heartbreaking for what this says about the world we humans have made. But I still find wonder in the stories these nests tell about the lives and circumstances of their architects and the deliberate choices they made in assembling the place where they will raise their offspring.
Vanya Rohwer is the curator of birds and mammals at the Cornell University Museum of Vertebrates.
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