I'm more fond of snakes than most people. My family and I enjoy finding garter snakes in our yard, and I consider it an added bonus to see water snakes in a river when I'm fishing. My daughter even keeps a corn snake for a pet. But I retain in my heart a special place for rat snakes. They are the largest nonvenomous snakes in the eastern U.S., and they get tame fairly quickly with handling.
Black rat snakes were common in the woods near my childhood home in suburban Cincinnati. My brother and I and our friends caught them regularly, and we were sometimes called upon by neighbors to remove them from garages.
Attached as I am to rat snakes, however, I had never wondered much about how climate change will affect them. University of Illinois researcher Patrick Weatherhead has, though.
In a collaboration that included three graduate students over the course of about 10 years, he assessed the likely consequences of a warming environment on rat snakes.
Fortunately for purposes of the study, the researchers did not need to figure out how to create a warmer environment for their subjects in order to test their hypotheses. Instead, they took advantage of the fact that rat snakes occupy a broad geographic range, and used latitude as a surrogate for climate change. That is, they compared the ability of rat snakes to regulate their body temperature through behavior in three populations representing the north-to-south extent of their range: Ontario, Illinois and Texas. What they found was that rat snakes in all three places will derive some benefit from a warmer climate.
Say, for example, future daytime temperatures in Illinois warm beyond the range that rat snakes prefer for activity.
What would they do?
For an answer, Weatherhead and colleagues looked to the behavior of rat snakes in Texas, where the climate of the present is approximately the same as the climate projected for Illinois within 50 years or so.
When daytime temperatures in Texas get too hot for foraging, the researchers found, rat snakes there wait until the cool of the night to go looking for food. Weatherhead expects that rat snakes in Illinois will follow suit, although the ones in his study were still active strictly during the day. (He notes that there is already other anecdotal evidence of snakes raiding birds' nests at night in Illinois.)
Increased nocturnal foraging may even provide a benefit to rat snakes. At night, they are more likely to catch adult birds on the nest and so eat them along with their eggs. In addition, rat snakes hunting at night might be less vulnerable to the animals that prey on them when they're active by day.
While the capacity to shift from hunting during the day to hunting at night may enable rat snakes in Illinois to cope with global warming, Weatherhead emphasizes that it's not likely to result in a plague of them. "They are not," in his phrase, "a universally well-loved group of animals." Their populations will still have to contend with diminishing habitat, high road mortality and the fact that people sometimes still purposefully kill them.
And what's good for rat snakes might be bad for other animals, especially the ones they eat and the ones that eat them. In Texas, for example, rat snake predation is already a problem for two species of endangered birds. "Things don't live in isolation," Weatherhead emphasizes. "It's crucial that we understand how the components of various ecosystems might be affected if we're going to work effectively to protect them."
Environmental Almanac is a service of the University of Illinois School of Earth, Society and Environment, where Rob Kanter is communications coordinator. Environmental Almanac can be heard on WILL-AM 580 at 4:45 and 6:45 p.m. on Thursdays.