Biologists study snake movement, mortality at Mingo

Tuesday, May 6, 2008
(LEFT) Missouri Department of Conservation intern John Hartleb (right) and Mingo National Wildlife Refuge Biologist Jason Lewis use radio telemetry to track the movements of 10 cottonmouths from their hibernaculum on the refuge's western border. (Paul Davis/DAR)

PUXICO, Mo. — Most people don't like snakes, regardless of their role in nature. For eons, tales have been spun that have given people a general disdain for and a bad impression of snakes.

Fear and misunderstanding are prevalent, leading some people to kill any snake they see, by any and every means.

That's a shame, said Jason Lewis, a wildlife biologist at Mingo National Wildlife Refuge near Puxico.

"Snakes serve a very important role in the ecosystem," he said. "Snakes are designed to control pest populations and they eat a lot of frogs, turtles [and] fish."

Reptiles and amphibians, Lewis added, are "very sensitive to disturbance, and can be used as indicators of environmental change."

Snake mortality has become a concern at the Mingo refuge because many are run over by vehicles, whether intentionally or not, during their spring and fall migration periods.

The concern has grown to the point officials have begun a study to determine just how snake populations in the refuge are being affected.

Cost-share grant

The U.S. Fish and Wildlife Service, which operates the Mingo refuge, has teamed with the Missouri Department of Conservation, Missouri State University, the Mingo Swamp Friends and others on a challenge cost-share grant to study snake movement and mortality at Mingo.

"We're concerned about the number of snakes being run over, and the whole idea behind the study is to minimize mortality," Lewis said. "We want to know, 'Are pregnant females being impacted more than males?'"

If they are, he said, that could potentially harm the snake population, because the females produce the young.

Lewis also said biologists want to find out what exactly triggers snake migrations.

The western cottonmouth, a venomous species native to the area, was chosen as the test subject "because we knew we had a healthy population," Lewis said.

In early April, Lewis and Missouri State University herpetologist Dr. Brian Green captured five males and five females at their hibernaculum, or winter hibernation location, along the rocky bluffs on the refuge's western boundary.

After the snakes were transported to a safe location, Green sedated eight of them and surgically implanted a flexible radio transmitter inside their bodies, near their tails.

The remaining two were sent to the university later for the procedure.

The transmitters will allow officials to use radio telemetry to track the snakes' movements over the course of the next year.

Officials also plan to capture and implant transmitters in five cottonmouths during the summer at the adjacent Duck Creek Conservation Area to include in their study.

After the cool weather moderated, the snakes were returned to the same location they were captured from.

Radio monitors

Now, Lewis, Missouri Department of Conservation natural history biologist intern John Hartleb and two interns from Three Rivers Community College will monitor the snakes' movements.

"We're going to look at the snakes' differential dispersal," Lewis said. "We want to find out, 'Do females disperse earlier or later than males?'"

Theoretically, Lewis said, the larger males should disperse from the hibernaculum earlier because their larger bodies are more able to tolerate spring's temperature swings.

Lewis said they also want to find out how far the snakes travel into the refuge's swamps and waterways.

With the warming spring days, Lewis said, the snakes should begin their migration out of the rocky bluffs and into the swamps any time now, and they'll check on the snakes' movements daily.

"It's going to take us literally hundreds of hours to track these snakes over the next several months," Lewis said.

In addition to using radio telemetry on the test snakes, Lewis said, officials will drive some roads daily to check for mortality.

Once the snakes are consistently in one area, Lewis said, they will scale back their monitoring, checking their movements weekly. Then, when the cottonmouths' breeding period begins in July, monitoring will be increased.

Then, in the fall, they will track their migration back to the hibernaculum.

During the course of the study, Lewis said, numerous types of data will be collected, including weather conditions, the habitat structure where snakes are located, how females with young move, how the young find the hibernaculum and more.

"With all the data, it should give us a better understanding of what they need," Lewis said. "We should be able to later determine the best conditions for migrations and close some roads ahead of time."

With the roads closed during the peak migration, the snakes can cross without being killed.

Because the radio transmitters implanted in each snake are designed to last one year, Lewis plans on recapturing each one next spring.

"We'll find the snakes again next spring and get the transmitters out of them," he said. The transmitters, Lewis said, will be refurbished and used again on different snakes.

Lewis hopes to continue the study for three years, but that, he said, "all depends on funding. Three years would give us a good data set."

Lewis is hopeful when the study is complete, snake mortality on the refuge and at Duck Creek can be greatly reduced.

"The job of any conservation agency is to provide a refuge for organisms that could potentially be in peril," he said. "If you don't know what's affecting them, you could eliminate a whole age class from a population."

Hartleb reiterated the importance of the snakes in Mingo's ecosystem.

"Everything has a place in the balance of life," Hartleb said, "and these snakes are very important predators."

Removing the snakes, Hartleb said, would adversely affect the whole ecosystem.

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