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

From the Spring 2025 problem of Dwelling Fowl journal. Subscribe now.

For many years, ornithologists have noticed birds like Nice Crested Flycatchers and Northern Home Wrens draping their nests with an uncommon materials: shed snakeskin. However they may by no means perceive why—till now.

In a research revealed in December within the journal The American Naturalist, a group of researchers at Cornell College and the Cornell Lab of Ornithology discovered proof that cavity-nesting birds use snake sheds to discourage would-be predators from consuming their eggs and nestlings.

The usage of snakeskin in fowl nests was lengthy seen extra as a curiosity than a topic worthy of scientific pursuit. However Vanya Rohwer, the research’s lead writer, believed there have to be some ecological motivation behind the habits.

“It’s not like that is leaves or dried grass,” says Rohwer, the curator of birds and mammals on the Cornell College Museum of Vertebrates. “Snakeskins are fairly uncommon to search out while you’re strolling round exterior. That is distinctive sufficient that birds are actually looking for this out.”

Rohwer and his collaborators started their research by testing a longstanding suspicion amongst ornithologists that cavity-nesting birds (like wrens) use snake sheds much more ceaselessly than open-cup nesters (reminiscent of robins and cardinals). After scouring the scientific literature, they discovered accounts of 78 fowl species from 22 completely different households bringing snakeskin to their nests. Certain sufficient, cavity nesters made up a disproportionate variety of these species. That instructed these birds should derive some evolutionary benefit from snakeskin that doesn’t assist open-cup nesters in the identical approach.

To determine what that benefit could be, the researchers examined a variety of hypotheses. By strategically putting strips of snakeskin (obtained from an area snake vendor) in some energetic Tree Swallow and Japanese Bluebird nests whereas leaving others unmanipulated, they had been in a position to take a wide range of measurements about how snakeskin impacts nest well being, together with the species of micro organism current within the nest and the variety of parasites (like lice) discovered on the nestlings. In every case, they discovered no variations among the many nests.

To check nest predation, the researchers wanted a unique method—one which wouldn’t endanger any actively breeding birds. In order that they created their very own synthetic nests, simulating cavity nests with nest containers and open-cup nests with inactive robin nests. The researchers arrange 147 synthetic nests in a pure space in Ithaca, New York, referred to as Monkey Run, putting two home quail eggs in every nest—however solely half additionally contained a chunk of snakeskin. Then, they left the nests unattended for 2 weeks, checking in each few days to see if the eggs had been broken by predators.

The outcomes had been hanging: Whereas the snake sheds had no impact on predation charges in open-cup nests, the researchers discovered that eggs in cavity nests augmented with snakeskin had been more likely to outlive the experiment. Rohwer says that this distinction could come up as a result of open-cup nests will be accessed and preyed upon by any variety of animals, however the small openings to cavity nests doubtless limit potential predators to small-bodied mammals like flying squirrels and chipmunks— species which can be hardwired to keep away from any signal of snakes.

Rohwer stresses that many questions on the usage of snakeskin in fowl nests stay unanswered, and whereas this research begins to elucidate the thriller, it additionally speaks to the necessity for additional analysis into how and why birds select their nesting supplies.

“To think about these birds as simply going out and randomly choosing up sure supplies, it’s approach too simplistic,” Rohwer says. “I believe that the extra we have a look at nests in nearer element and particularly understanding the supplies that birds are utilizing, we’re simply going to study an increasing number of about how birds are mitigating challenges related to replica.”