by In 1889, the naturalist Allan Octavian Hume wrote that he was amazed by the macabre decorations he observed in many bird nests: strips of dried snake skin.
‘Are birds superstitious, I wonder? Do they believe in charms?” he wrote in ‘The Nests and Eggs of Indian Birds’. If not, why did so many birds use pieces of snakeskin to decorate their nests? Hume and some of his contemporaries had a hypothesis: the snakeskin scared away predators.
A new study suggests they were on to something: After analyzing centuries-old bird nest data and observing more than 140 nests with and without snakeskin, researchers reported last month in The American Naturalist that in some types of nests the presence of snakeskin is enormous. reduced the risk of predators stealing the eggs.
All reptiles shed dead skin cells as they grow, but snakes shed skin in one large chunk from their entire body. However, finding a snakeskin in the wild can be tricky, says Vanya Rohwer, curator at the Cornell University Museum of Vertebrates and author of the study. This scarcity of snakeskin makes it all the more remarkable that so many birds use it in their nests.
‘How on earth do they like it? And why do they invest all this time to bring it back to their nests?” said dr. Rohwer.
Dr. Rohwer pored over digitized historical data on bird nesting behavior, including handwritten observations of nests from more than a century ago. He and his colleagues found that cavity nesters – birds that build their nests in holes in structures such as trees and cliffs – are six and a half times more likely to incorporate snakeskin into their nests than species that create more ‘classic’ bowl-shaped nests.
Based on this information, Dr. Rohwer conducted a series of experiments to “try to understand what the benefits of shed snakeskin might be.” He examined the microbes and larger parasites in nests with and without snake skin to see if the skin repelled bugs like fleas and mites or reduced the nest’s harmful microbes. There didn’t seem to be any connections. “The other idea we looked at was an idea of nest predation,” said Dr. Rohwer.
In a wooded area called Monkey Run near the Cornell campus in Ithaca, NY, Dr. Rohwer quail eggs in 65 nest boxes, which resemble cavity nests, and 80 empty robin nests, which are open-headed nests. He added snakeskin to half the nests and spent the next few weeks checking them with a ladder. “My wife called me Ladder Man,” he said.
During his time as Ladder Man, Dr. Rohwer something surprising: While the snake skin didn’t seem to make much difference to the safety of the eggs in the open nests, the scaly leftovers made a big difference in the nest boxes.
“The cavern nests with snakeskin were much more likely to survive a fourteen-day incubation period compared to a cavern nest without snakeskin,” he said. Snakeskin in particular seemed to deter small mammals such as mice, which are known to catch eggs.
This discovery raised additional questions. “What’s scary about snakeskin? Is it the smell of snakeskin? Is it the sight of snakeskin for these small mammals? said dr. Rohwer.
Ross Crates, an ecologist at Australian National University who was not involved in the study, noted that other research had found that some birds hissed to ward off predators to their nests. “Pretending that there is somehow a snake in the nest benefits these small, cave-nesting birds, which have less capacity to actually physically defend the nest from larger, primarily mammalian predators,” suggested Dr. Crates.
Dr. Rohwer said nests have been overlooked in scientific research, in part because they are difficult to observe and study. Digitized data sets like the ones he and his colleagues used help researchers make discoveries. “We’re just now really starting to look at some of the unique materials in bird nests,” he said.
