Garter Snake Study


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Photo Credit: Ohio Division of Wildlife

Eastern plains garter snakes can be found in the prairie regions of the United States and Canada. During the warmer, drier months of the year, these serpents burrow underground or slip beneath rocky roadsides to stay cool.

In the state of Ohio, the Eastern plains garter snake (Thamnophis radix) has been a state endangered species since 1974. And 24 years later, a study reported a 94% decline of the snakes.


“We were working at a remnant prairie site which has the eastern most population of the plains garter snake in the country and discovered that the snake had undergone a drastic decline in the last 15-20 years,” says Doug Wynn, a retired high school teacher, who taught research classes that conducted projects for the Ohio Division of Wildlife. “We do not know why the snakes are declining… We have looked at weather changes over the years, food availability, competition from common garter snakes, habitat loss and loss of genetic diversity… This is one of those investigations that every time you ask a question five more come up. It is possible that the population may experience natural, long-term fluctuations.”

According to Carolyn Caldwell, a representative for the Ohio Division of Wildlife, there are less than 100 adult Eastern plains snakes in the wild. Both the Cleveland and Columbus Zoos have also confirmed the decline of the plains garter snakes’ population. Back in 1999, these two zoos were brought into an ongoing study to restore a self-sustaining population of plains garter snake. 

“We feel it is important to conserve this snake because it is a remnant prairie species and is part of our natural heritage,” says Wynn. “If it does turn out that the species has declined as a result of a natural population fluctuation, then that is important scientifically.”

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Photo Credit: Doug Wynn

According to the Ohio Division of Wildlife, Eastern plains garter snakes are generally hardy in captivity. Adults snakes are housed together, while juveniles and neonates are caged individually. Because this snake’s natural outdoor environment has fluctuating temperatures, the zoos adjust the captive snake buildings to 70-80 degree Fahrenheit during the day and about 65 degrees at night. Adults and juveniles are fed twice weekly, while neonates are offered food three times. The Plains garter snake mates in the springtime.

In the beginning of this conservation program, captive-born snakes were simply released into the wild. Wynn notes that these individuals took off into the wild and they never saw them again.

Eastern plains garter snakes have many predators in the wild, from birds of prey to predatory mammals like foxes, domestic cats, coyotes and skunks.

“And we questioned how they [released snakes] might be dealing with suddenly being into the wild… We know that snakes can stress out over things,” adds Winn. “Snake keepers have known for years that just having a hide box in a cage may be enough for a newly captured snake to begin feeding in captivity. Thus we felt that it might be better to release them more gradually.”

So Wynn built “soft release” cages to help reduce the snakes’ stress. The adult, captive-born snakes were transferred to these cages and allowed to acclimate to the wild for a couple of months in a safe environment. Before their release, the collaborative teams implanted transmitters in the snakes to track their movements. Then, the snakes were let free in the Killdeer Plains Wildlife Area. “”Once we started releasing older, and larger individuals, they were large enough to carry transmitters,” Wynn explained. “We are now starting to look at how far they move, whether soft releases are better, what type of habitats they utilize, possible differences in sexes, etc.”

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Photo Credits: Doug Wynn

By utilizing their tongue to follow chemical prey trails, Eastern plains garter snakes are able to feed on a variety of pint-sized prey, like amphibians and earthworms. These serpents also look for visual cues while hunting.

Although a mild-tempered species, plains garter snakes have several defense mechanisms. First, they will attempt to flee when threatened. Should they continue to feel endangered, they will defecate and musk a potential predator. If captured, this snake may might bite or regurgitate a meal.

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Photo Credit: Doug Wynn

Since 1999, 175 Eastern plains garter snakes have been bred in captivity and released in the wild. According to ODW’s Carolyn Caldwell, “Nenonates – snakes released shortly after birth in captivity – are very small in size and have a higher mortality rate.” Free-ranging snakes have a 16% survival rate during their first year in the wild. But the survival rate of head-started snakes (individuals over a year of age at the time of release) could be possibly 40%. “So, in theory, releasing snakes that are older and have a larger body size than neonates enhances our ability to increase the wild population,” says Carolyn.

The Ohio Division of Wildlife’s Endangered Species and Wildlife Diversity Program, Ohio Department of Natural Resources, Westerville North High School Field Study Class, Liberty University, Northern Illinois University and the University of Tennessee are also supporters of this project. Funding is generated from the sale of the Ohio Wildlife Legacy Stamp.

Learn more about animal conservation and out this National Geographic gallery of snake images.