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Eastern Indigo Snake Research--The Early Years

By James Altiere, Regional Hunter Education Coordinator, Alabama Division of Wildlife and Freshwater Fisheries

The Eastern indigo snake (Drymarchon couperi) is the largest snake found in North America. The adult snake can reach lengths greater than 8 feet. Its scales are a glossy bluish black (thus the name indigo) with a light cream to reddish coloration around the cheeks, throat and chin. The indigo snake is non-venomous, and is one of the main predators of the Eastern diamondback rattlesnake (Crotalus adamanteus). Mainly because of the loss of suitable habitat, the indigo snake is listed as a species threatened with extinction.

It is well known that indigo snakes use the burrow of gopher tortoises (Gopherus polyphemus) to escape the cold temperatures of winter. On warm, sunny days in the winter, the snake can be found basking in the sun near the mouth of a gopher tortoise burrow.

A few years ago, research was needed to learn more about the Eastern indigo in order to reintroduce the snake to preferable habitats and stabilize the population. Therefore, adult snakes were placed in a breeding colony housed at Auburn University. This breeding colony successfully produced baby indigo snakes. To find out more about the indigo snake, radio telemetry was used. Adult indigos were marked and a radio transmitter with the antenna exposed was placed under the skin of the snake. The snake could be tracked using a radio receiver tuned to a particular snake’s frequency. This method worked fairly well with adult snakes, but did not work at all with hatchlings.

At first it was thought that releasing the hatchlings in and around gopher tortoise burrows was the right approach. But after documenting indigo snake cannibalism (adults ate the smaller juveniles), it was determined that more needed to be learned about the hatchling snakes and what type of habitat was most favorable for their survival. A technique had to be developed for implanting small radio transmitters in hatchling snakes.
One proposal was to place a transmitter inside the body cavity, with the antenna threaded underneath the skin by the use of a catheter. The thought was that with the transmitter in the body cavity and the antenna under the skin, nothing could catch on debris and the snake’s skin would not wear, so the transmitter would stay on the snake.

Before they could insert the transmitter, biologists had to devise a way to anesthetize the snake. A chamber was built using plywood, Plexiglas and a simple sink drain. One end of the chamber was a plunger-type wall that would allow the volume of the chamber to be changed. The sink drain was embedded and sealed in the top of the chamber. When a snake was selected to be put to sleep, the snake was weighed and then placed in the chamber. The volume of the chamber was then set, based on the size of the snake. A cotton ball was place in the sink drain and the proper amount of anesthesia was put on the cotton ball. The fumes from the anesthesia, being heavier than the surrounding air, would fill the chamber and the snake would go to sleep. The crudely designed apparatus worked surprisingly well.

A corn snake was selected as a surrogate species. The radio transmitter was successfully implanted and the corn snake was released at a nearby study area and followed using radio telemetry. Unfortunately, the corn snake was eaten by a king snake, but that’s for another article. This method, however, paved the way for a study designed to learn more about the habitat needs for a successful release of hatchling indigo snakes.
Radio transmitters were successfully implanted in a large sample of hatchling indigo snakes. The snakes were released on St. Marks Wildlife Refuge in Florida. A graduate student followed the radio-equipped snakes and learned the types of habitats used by the baby snakes. This information gave rise to the current re-introduction strategies being conducted today to restore the Eastern indigo snake in Alabama.


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