College of LAS « Illinois

Animal Biology

Snakes on the Plains!

LAS researchers track snakes in Illinois, Texas, and Canada.


A 6-foot-long rat snake was sliding down a tree trunk when Patrick Weatherhead first spotted it.

Weatherhead, a University of Illinois animal biology professor, was tracking snakes with a graduate student at the time. However, just as the student reached out for the rat snake, the serpent released the back end of its body from the tree. In an instant, it coiled on the side of the tree, like a spring ready to release—which is exactly what it did.

The rat snake launched itself into the air and went flying right by them at eye level. The snake was fleeing, not attacking, but it was an alarming maneuver nonetheless—just one of many memorable snake encounters since Weatherhead began doing research on them more than 25 years ago.

While the entertainment world has sometimes been obsessed with snakes in the most unnatural of places—Snakes on a Plane—Weatherhead’s expertise has been a snake’s natural habitat. In particular, he has zeroed in on the habitat of rat snakes, a non-venomous snake that sometimes imitates a rattlesnake’s rattle by vibrating its tail against dry leaves.

Weatherhead says he started working with rat snakes in a backdoor way, through his bird research. In the early 1980s, he was studying how much risk birds took in defending their nests from predators. To observe how birds interacted with rat snakes, he had transmitters designed that allowed him to track the snakes’ movements.

“But snakes turned out to be such interesting subjects in their own right that I began doing snake research, taking advantage of rat snakes’ distribution over a wide range of latitude to study their thermal ecology.”

“Thermal ecology” refers to how temperature changes affect habitat selection and population numbers.

Weatherhead’s team currently works in three different regions—southern Ontario in Canada, southern Illinois, and Texas. In Canada, he’s looking at ways to preserve the dwindling rat snake populations, while in Texas he’s studying the opposite problem. In Texas, rat snakes are plentiful, but they pose a threat to two endangered bird species.

U of I researchers have found that rat snakes have an affinity for “living on the edges”—places where forests meet open areas, such as swamps or fields. This is only fitting since Weatherhead cultivated his love for wildlife as a youth by “living on the edges” himself. His home was in town, but his family always lived on the edge of natural areas—with wildlife just out the back door.

“Edges” provide the ideal habitat for snakes to control their body temperature, he explains. Because snakes are “ectotherms,” they must use external sources, such as the sun’s heat, to keep their body temperature at the proper level. By living on the edge, if a rat snake needs to warm its body, it moves into the open field. But if it needs to cool down, it can slither into the forest shade.

In addition to monitoring snake behavior, Weatherhead’s team uses the implanted transmitters to keep track of their body temperature. Among many findings, they have discovered that colder climates slow the growth of snakes, thereby slowing their maturation and reproduction rates.

To carry out this research, Weatherhead’s team goes into the field with receivers to track and map the location of as many as 25 different snakes every day. Working with rat snakes so much, Weatherhead says he has been bitten many times. But with rat snakes, that’s not much of an issue.

“I’d much rather be bitten by a rat snake than a mouse, which have teeth intended for breaking through hard seeds,” he says. “A rat snake bite will break the skin, but just barely.”

Winter 2008