If you haven’t been paying attention, the summer season is slowly shifting into fall with decreasing temperatures and shortening day lengths. Birders know about these things as they watch migrating birds moving through the state to escape cold weather. Hunters realize that elk and deer will be moving to different areas of their range to avoid deep snow. Perhaps you’ve wondered, “So what do snakes do when the cold weather season approaches?” Because snakes cannot produce their own body heat, they must find a way to stay out of freezing weather until spring. The only place available to avoid freezing is underground, and between now and October, snakes at South Table Mountain will begin the autumnal migration, a gradual movement which directs them to places they know will be below the frost line and give them protection against freezing.
Most snakes enter a subterranean location by mid-November, staying put until perhaps late March, a duration of time called “hibernation”. The location where snakes reside for the winter below the frost line is termed a “hibernaculum” or “den”. Hibernacula (plural of hibernaculum) are critical to the survival of snake species living in temperate zones with cold winters. Without hibernacula, snakes would not survive to reproduce and prey on species, such as rodents, which need the pressure of snakes, birds, and mammals to keep them in check.
One example of a hibernaculum with an entrance under a boulder. Note there are three rattlesnakes visible! Hibernacula are very difficult to identify without snakes present and should remain undisturbed. Photo provided by Derek Carlson
--You may ask, “Now, where would a snake find a suitable subterranean hibernaculum in the vast area of their home range?” Snakes take full advantage of ways to get underground by utilizing rodent burrows of all kinds, such as those belonging to thirteen–lined ground squirrels, prairie voles, and prairie dogs, as well as subterranean passages between rocks that take them deep underground. In areas of their range where hibernacula are not found easily, snakes have learned over hundreds of years or more to use a particular location that supports survival. Up to hundreds or thousands of snakes use this hibernaculum, also known as an ancestral den. In the Front Range area of Colorado, the geologic formations that make up these mountains create large numbers of underground cavities within rocky hillsides that are easily accessed by snakes. Locating a suitable hibernaculum is then relatively simple. Young of the year juvenile snakes commonly follow the scent trail of adult snakes in the fall to discover the best routes to the hibernaculum, or they simply use the nearest rodent burrow and hope that it’s deep enough.
Commonly, several different species of snakes, such as bullsnakes, rattlesnakes, garter snakes, and racer snakes occupy the same hibernaculum during the winter without conflict, and in the spring they all go their own way. With some snake species, such as rattlesnakes and garter snakes, a mild winter day may allow a few individuals to surface at the hibernaculum opening and enjoy the warm sun without exposing themselves totally to predators. Otherwise, most snakes remain underground and out of sight until the warming days of spring begin to heat the soil and rocks, which eventually warms the interior of the hibernaculum and out they come!
Stay safe on the trails as rattlesnakes begin to move to their hibernacula! Photo by Ryan Borgmann
What should you do if you encounter a rattlesnake on a trail?
What should you do if you are bitten by a rattlesnake?
How should you protect your dog?
Adaptation Environmental Team: Bryon, Joe, and Kelly