The Nachusa Grasslands near Dixon, Ill., just a 45-minute drive from the NIU campus, had a new…
Most Midwesterners have never encountered a rattlesnake—but the snakes do indeed exist in these parts, though their numbers are dwindling.
While you won’t find them slithering along Chicago’s Michigan Avenue, the Eastern Massasauga, a small North American rattler with a distribution centered around the Great Lakes, was found in wetland areas of Cook County until as recently as 2010, according to Northern Illinois University biological sciences professor Richard King.
King and his former student Eric Hileman have published a new study on the life history of the Eastern Massasauga, revealing important local climate impacts on the snake that should be carefully weighed when developing conservation strategies. The Eastern Massasauga was listed as threatened under the U.S. Endangered Species Act in 2016.
“Our results provide evidence that climatic variation in the Great Lakes region strongly influences body size, individual growth rates and key aspects of reproduction,” says Hileman, first author of the study published Feb. 14 in PLOS ONE, a journal of the Public Library of Science. Hileman earned his Ph.D. in biological sciences from NIU in December and is now a postdoctoral fellow in biology at Trent University in Ontario, Canada.
“We show that life-history traits vary significantly across the species’ range,” Hileman adds. “This is important for conservation because it suggests that extinction risk models and conservation management strategies that fail to account for life history variation may be unreliable and ill-suited for local populations.”
Hileman, King and more than 40 co-authors gathered and synthesized more than a century of data on the snakes from 47 study sites representing 38 counties across the range of the Eastern Massasauga. While most of the data was culled from studies conducted from the mid-1990s forward, some dated as far back as the late 1800s.
The scientists found strong evidence for geographic variation in six of nine life-history variables. Among the findings:
- The average body size of the snake and the size of its offspring increased with increasing mean annual precipitation, with wetter climates inferring larger prey abundance.
- Litter sizes decreased with increasing mean temperature, and increased by one offspring for each 1.89-degree increase in latitude, even when maternal size was held constant.
“It’s been rare to look within a species and show that these patterns exist,” King says. “The study results demonstrate that a one-size-fits all conservation strategy is not appropriate. Rather, assessments of extinction risk and the design of management strategies need to account for geography.”
The Eastern Massasauga snakes, which do indeed have rattles, are generally found in wet prairies or sedge meadows, where the reptiles employ a sit-and-wait strategy to catch and feed on small mammals. Adult size ranges from about 2 feet to 2 ½ feet in length. While venomous, the snakes are not particularly aggressive or dangerous to work with.
“You’re not likely to encounter them unless you’re looking for them,” King says. “It’s easy to walk right by one. They’re very cryptically colored to look like dead leaves and cattails, so they blend in exceedingly well.”
While the population of the Eastern Massasauga has been steadily declining, its range has been shrinking as well. As recently as the 1970s, some states had bounties on the snake.
Once widespread in Illinois, the reptiles suffered habitat loss from extensive drainage of land for agriculture and development. With concerns over whether they would persist in the wild, the remaining snakes in Cook County were taken into a captive breeding program, King says.
“In Illinois, they’ve nearly blinked out entirely,” he adds. “We’re probably down to one location in the southern part of the state that has a stable population. They seem to have stronger holds in Michigan and southern Ontario.”
Sources for life-history information included study sites in Illinois, Indiana, Wisconsin, Michigan, Iowa, Ohio, Pennsylvania and New York, as well as Ontario, Canada. The study authors believe findings will aid Eastern Massasauga recovery efforts.
“The life-history parameter estimates will be essential for improving models related to extinction risk and climate change,” Hileman says. “The results from these predictive models can subsequently be used to develop site-specific management strategies.”
Whether the snakes should ever be re-introduced in the Chicago region is a question for future debate, King adds.
“It’s a question that goes beyond the biology of the species because of public perception and a risk that would need to be addressed as well,” he says. “But to have self-sustaining populations in Illinois lasting into the future, we need more than one population.”