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Rattlesnake Research

Rattlesnake Research Program at the Lindsay Wildlife Museum

by Linda Orchard-Hays
Mount Diablo Review, January 1999

Rattlesnake Research

Northern Pacific Rattlesnake, North Gate Road | Clayton Worsdel

Rattlesnakes. Most people are afraid of them and yet many of us have never seen one in the wild. These shy creatures prefer to remain out of sight, and do us the courtesy of giving a warning when we get too close. Although rattlesnakes can hear very low frequencies and vibrations, their rattles exist for the benefit of the predator. Rattlesnakes’ primary predator is man, who kill them out of fear and ignorance. However, they are also killed by hawks, eagles, roadrunners, coyotes, bobcats and kings snakes. 

There are 29 species of rattlesnake within North and South America. The one most common to California is the western rattlesnake (Crotalus viridis); it ranges from south-western Canada to Chihuahua, Mexico and as far east as western Iowa. There are nine sub-species of this snake; the most common one in the Bay Area is the northern Pacific rattlesnake (Crotalus viridis oreganus). 

Although rattlesnakes can be aggressive when hungry or threatened, they do not often bite humans. A bite with venom (venom is not always injected) can cause swelling, necrosis, fever, and nausea. The only way to treat a bite is to get to a hospital within four hours and receive anti-shock and anti-venom treatment. 

The northern Pacific rattlesnake, according to Carl Ernst’s description, is dark gray, olive, yellowish brown, brown or black and has dark hexagonal or circular blotches with light borders (from Venomous Reptiles of North America). The average length ranges from 1.5 feet to 2.5 feet with the maximum length being just over 5 feet. They eat small rodents, birds and lizards and live for 16-20 years. 

The females generally give birth every 2 years although it can vary from
every year to every third year. The gestation period is 110 days and they give birth to an average of 10 live young. Generally, the females will live in maternity colonies throughout the year and not migrate to the summer feeding ground.

The western rattlesnake can be found in a variety of habitats such as woodlands, scrub areas, grasslands, desert margins or sand dunes. Its main requirement is having adequate hiding spots, such as ground squirrel burrows or rocky outcroppings, within migratory distance. These snakes have a summer feeding area, a winter hibernation site and a migration corridor between the two, and they are highly tenacious to their territory. If, for example, a house is built on their migration route, those homeowners may find rattlesnakes in their yard each year.

The territories of western Pacific rattlesnakes are about .05 to .025 square miles. They emerge from hibernation in the early spring and shortly thereafter migrate to the summer feeding area. They then return to the hibernacula in October and hibernate through the winter. In this area, the snakes may briefly come out of hibernation on a warm winter day. The distance between the summer feeding ground and the winter hibernacula depends primarily on the climate. Cornell professor Dr. Harry Greene has found that in Arizona this species stays in the same territory year-round while in Wyoming it can migrate over five miles. It is not yet known how far they migrate in this area. 

That is one of the questions that we hope to find an answer with the wildlife research project at the Lindsay Museum. If we can determine the location of the territories and migration routes we can be better informed about our activities at certain times of the year. 

The Lindsay Wildlife Museum has a Wildlife Research Program consisting of five different projects. Through a series of classes, each project trains volunteers in scientific observation and data collection. The volunteers then collect data to answer a specific scientific question for a partner organization. The program therefore simultaneously provides an educational opportunity and scientific research. For each project there can be more than one partner organization. 

The rattlesnake project has four partners: Lindsay Wildlife Hospital, Ohlone-Sunol Wilderness, Black Diamond Mines Regional Preserve, and Mount Diablo State Park. The project is studying two questions: 1) What are the movements of a snake brought into the hospital after it has been rehabilitated and released? 2) Where are the migration routes and territories of rattlesnakes in this area? 

The first question will help us understand if a snake is able to orient back to its territory and/or be successful once it has been removed and released. A snake must be released within three miles of where it was found. However, since a western rattlesnake only moves a couple of meters each day, three miles may be too far away from its territory for it to be successful. 

The second question is more long-range and will require many studies; however, it can lead us to understand the habitat needs of this animal and help us minimize human impact. The snakes are studied by implanting them with a radio transmitter. Each snake can then be tracked using a receiver and an antennae. 

Currently, the project has one young adult male snake that has been implanted and released at Mount Diablo State Park. In the spring, when the snakes become more active, volunteers from the project will be assisting at Ohlone-Sunol Wilderness with a similar project already in place there. We hope that in the future more parks n space areas will do research on these animals to promote our understanding and preserve their habitat.

If you are interested in learning more about these projects or becoming a volunteer please contact the Lindsay Wildlife Museum at 925-935-1978.

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