Why do birds build nests with shed snake skins? | ECOVIEWS

Q: My husband was excited when he witnessed a robin building a nest by recycling a shed skin from a snake that lives at the foundation of our house in Clarksville, Tennessee. We're not sure exactly what kind of snake. He's 3 feet long and darkish, but is kind of shy and goes back in the hole when we get close. We were surprised that a bird would have anything to do with any part of a snake, living or dead. It was amazing how much skin the bird stuffed in its beak before flying off to the nest, where it incorporated the shed skin in with twigs and dead grass. Why would a bird do such a thing?

A: Great observation! Several bird species use the shed skin of a snake during nest building to scare off predators. I was not aware robins had joined the ranks of those that adorn their nests that way. The great crested flycatcher places a shed snake skin in its nest and leaves it there until the young have fledged. Tufted titmice and blue grosbeaks will do the same on occasion. Flycatchers, which nest in tree holes (or bird boxes), will often drape a shed snake skin on the outside of the nest cavity and will weave part of it into the nest itself.

When asked a similar question a few years ago about birds using snake skins in their nests, I referred to a study by ornithologists Elizabeth Medlin and Tom Risch of Arkansas State University. They speculated that the snake skin is a deterrent to would-be egg predators that might themselves become prey to snakes. The scientists conducted convincing research suggesting the presence of a snake skin as a greeting card was perceived as a warning sign by what they identified as a predatory culprit.

Two species of animals that encompass most of the geographic nesting range of great crested flycatchers are rat snakes and flying squirrels. Flying squirrels will eat bird eggs, and rat snakes will prey on flying squirrels. Rat snakes would also eat a bird egg, but flying squirrels are probably a greater threat.

The investigators put up 60 nest boxes and placed quail eggs and simulated eggs of modeling clay in each box. They placed one or more snake skins in the nest in 40 of the boxes; 20 nest boxes had no snake skin. The results supported the contention that snake skins deter flying squirrels from entering a bird nest and eating the eggs. None of the 40 nests with snake skins were attacked. Flying squirrels ate eggs in 20% of the nests without snake skins.

Brett DeGregorio, at the time a doctoral student conducting research on snake predation on birds at the University of Georgia’s Savannah River Ecology Laboratory, observed what he called “a sad twist” on bird behavior that attempts to use shed snake skins to ward off predators. According to Brett, “Birds, particularly blue grosbeaks, on the Savannah River Site have certainly adopted this strategy [but] we see most of our grosbeaks incorporating cellophane wrappers, flagging tape, or other bits of litter into their nests. Perhaps they are fooled by these clear bits of debris into thinking they are snake skins.”

A future goal of Brett’s research is to determine if “blue grosbeaks that successfully incorporate snake sheds in their nests are more likely to avoid predation” of their nests. Or will a piece of cellophane effectively fool a nest predator?

Despite a nationwide interest in birdwatching, many ecological mysteries about birds remain to be solved. The observation about the robin adds to our knowledge of which birds use snake skins. And Brett’s research may provide an example of how human litter is negatively affecting the natural world. By the way, the snake living under your house’s foundation is probably a rat snake. They love to eat flying squirrels.

Whit Gibbons is professor of zoology and senior biologist at the University of Georgia’s Savannah River Ecology Laboratory. If you have an environmental question or comment, email ecoviews@gmail.com.

This article originally appeared on The Tuscaloosa News: Why do birds build nests with shed snake skins? | ECOVIEWS