As a wildlife biologist I have spent 35 years studying birds and reptiles. Because of lack of fear, but deep respect, of rattlesnakes I am often asked to move a snake by a neighbor. I use snake tongs and a snake hook to safely move the rattlesnake. Once it is in the bucket with a good security lid and ready for transport there is usually a question I am asked. Do I think there is a rattlesnake den on their property? The answer is usually no. Seeing one snake does not mean you have a den. I hope to answer some questions people have asked about snakes and their dens in this blog.
First I think we need to define denning. It is the gathering of snakes into at particular point for winter hibernation. The snakes come from widespread summer ranges. Rattlesnakes are not the only snake to den. In fact rattlesnakes are known to den with other species of snakes such as the bullsnakes, milksnakes, racers, gartersnakes and copperheads. The benefits of moisture and heat conservation that rattlesnakes gain by denning would likewise accrue with any other snake that den with them.
Denning proclivities are greater in the northern and in higher altitudes, because these protective refuges are obviously more necessary due the cooler and longer winter months. In the south, where winters are milder shorter hibernation cycles occur, and may be interrupted by occasional warm spells.
Where snakes den depends entirely on the habitat. Where there are rocky formations the snakes seek deep caverns or crevices. In the plains, the snakes use the holes of mammals, particularly favored are prairie dog holes. The temperature not only affects the duration of hibernation, but the depth of the den. The cooler the weather, the deeper the den will be located. The snakes need to be below the frost line. The snakes also prefer south facing slopes in rocky areas. This protects them from cold northern winds and southern slopes receive more sun keeping the den warmer.
The size of the den depends on topography and climate. Where suitable sites are widely separated, populations tend to be larger with reports of 1000 rattlesnakes congregated in a single den. Even where good refuges are located close together the need for warmth and the gregarious nature of rattlesnakes lead to larger denning in the north. Larger dens also tend to be in rock formations. Where rattlesnakes utilize mammal dens the dens are temporary. The snakes have no way to keep the galleries clear and the den eventually collapses.
In dens that have been opened up by road or mine excavations the snakes are found to lie torpid and virtually motionless in groups of masses or “balls”. There have been observations of snake balls one foot in diameter and containing hundreds of snakes.
In the fall, it seems that larger and older snakes are the first back to the den. It is believed that the older snakes leave a trail for the younger snakes to follow back to the den.
Scientists believe another benefit of denning may be a level of protection against enemies. When the snakes are congregated in the dens they seem to be able, possibly by movement, to transmit a sense of alarm to each other. The last benefit believed to come from denning is the ease of finding a mate in the spring.
Much more study of denning snakes is needed. With new tagging techniques and the smaller size of cameras more information about denning will soon be learned. Even now one fact is clear, denning is an important aspect of a rattlesnake’s life and can be the difference of life or death.