Why Do Birds Put Snakeskin in Nests? It May Warn Away Predators

From the Spring 2025 issue of Living Bird magazine. Subscribe now.

For decades, ornithologists have observed birds like Great Crested Flycatchers and Northern House Wrens draping their nests with an unusual material: shed snakeskin. But they could never understand why—until now.

In a study published in December in the journal The American Naturalist, a team of researchers at Cornell University and the Cornell Lab of Ornithology found evidence that cavity-nesting birds use snake sheds to deter would-be predators from eating their eggs and nestlings.

The use of snakeskin in bird nests was long viewed more as a curiosity than a subject worthy of scientific pursuit. But Vanya Rohwer, the study’s lead author, believed there must be some ecological motivation behind the behavior.

“It’s not like this is leaves or dried grass,” says Rohwer, the curator of birds and mammals at the Cornell University Museum of Vertebrates. “Snakeskins are pretty rare to find when you’re walking around outside. This is unique enough that birds are really seeking this out.”

Rohwer and his collaborators began their study by testing a longstanding suspicion among ornithologists that cavity-nesting birds (like wrens) use snake sheds far more frequently than open-cup nesters (such as robins and cardinals). After scouring the scientific literature, they found accounts of 78 bird species from 22 different families bringing snakeskin to their nests. Sure enough, cavity nesters made up a disproportionate number of those species. That suggested these birds must derive some evolutionary advantage from snakeskin that doesn’t help open-cup nesters in the same way.

To figure out what that advantage might be, the researchers tested a number of hypotheses. By strategically placing strips of snakeskin (obtained from a local snake dealer) in some active Tree Swallow and Eastern Bluebird nests while leaving others unmanipulated, they were able to take a variety of measurements about how snakeskin affects nest health, including the species of bacteria present in the nest and the number of parasites (like lice) found on the nestlings. In each case, they found no differences among the nests.

To test nest predation, the researchers needed a different approach—one that wouldn’t endanger any actively breeding birds. So they created their own artificial nests, simulating cavity nests with nest boxes and open-cup nests with inactive robin nests. The researchers set up 147 artificial nests in a natural area in Ithaca, New York, called Monkey Run, placing two domestic quail eggs in each nest—but only half also contained a piece of snakeskin. Then, they left the nests unattended for two weeks, checking in every few days to see if the eggs were damaged by predators.

The results were striking: While the snake sheds had no effect on predation rates in open-cup nests, the researchers found that eggs in cavity nests augmented with snakeskin were much more likely to survive the experiment. Rohwer says that this difference may arise because open-cup nests can be accessed and preyed upon by any number of animals, but the small openings to cavity nests likely restrict potential predators to small-bodied mammals like flying squirrels and chipmunks— species that are hardwired to avoid any sign of snakes.

Rohwer stresses that many questions about the use of snakeskin in bird nests remain unanswered, and while this study begins to explain the mystery, it also speaks to the need for further research into how and why birds choose their nesting materials.

“To think of these birds as just going out and randomly picking up certain materials, it’s way too simplistic,” Rohwer says. “I think that the more we look at nests in closer detail and specifically understanding the materials that birds are using, we’re just going to learn more and more about how birds are mitigating challenges associated with reproduction.”