The "Cold-Blooded" and the Cold
Unlike their endothermic counterparts, such as humans, rattlesnakes have no way to internally regulate their body temperatures. This is why we often see reptiles behaviorally regulating temperatures by basking in the sunlight in the mornings or hiding when temperatures are outside of their comfort zone. Snakes generally can survive external temperatures ranging from 60-90 degrees Fahrenheit. But, what happens when the environment reaches temperatures below 60 degrees?
As the weather begins to cool and the snow begins to fall in the northern regions of the country, rattlesnakes have made their preparations for winter. But, depending on location, those preparations may look a bit different. Here in Florida, rattlesnake species will typically find places underground to hide on cooler days to keep warm, but will often emerge on warm winter days to bask. This is a common behavior around the southeast United States as temperatures rarely reach below freezing and cooler days are sprinkled with sunny 60-70 degree weather in between. Rattlesnakes, like many other reptiles, have this super cool ability to lower their metabolism and locomotion to survive the cold temperatures that winter brings. This is commonly called brumation, which is essentially the reptile version of hibernation, although in recent years, brumation and hibernation seem to be used interchangeably for reptiles. During periods of brumation, rattlesnakes will not eat or move around much at all in order to conserve their energy reserves.
In contrast to popular belief that snakes won't be out and about during the winter, brumation/hibernation allows for reptiles to increase metabolic activity/locomotion when temperatures raise during the winter months and then return to a lethargic state as the weather cools again. For example, a study conducted in Tennessee found that timber rattlesnakes in their study moved an average of about 6 times during the winter months and travelled about 145 meters total for the winter. They also found that although much of the movement was below ground, about 80% of the snakes surveyed made movement above ground at least once during the winter. However, in areas of rattlesnake ranges where it is colder more consistently during the winter, some biologists believe they behave more like mammals and stay in their dens or winter refugia sites the entire duration of the winter (normally from about October to March) in this state of torpor.
Rattlesnakes exhibit some interesting behaviors when it comes to overwintering. For instance, many studies have documented high site fidelity among some rattlesnake species, meaning they often return to the same den site every year or within 1 meter of the original den location to find refuge. Check out this study done on timber rattlesnakes to learn more about site fidelity. Additionally, some species have been documented using communal dens. Communal denning was first recorded in prairie rattlesnakes in the 1950s, but has since expanded to reveal even more interesting social behaviors among rattlesnakes. For example, a study completed in the montane forests of the Southwest United States by Amarello concluded that some adult Arizona black rattlesnakes exhibit preferences for denning with certain individuals by using an animal behavior model called an association index. If you're interested in learning more about rattlesnake communal den sites, check out this compilation of studies from Rattlesnakes of Arizona. Another study by Georgia State University completed in Arizona that looked at communal den sites of western diamondback rattlesnakes found adult rattlesnakes emerging from den sites after a cold rain shower even when the temperature was 37 degrees. Prior to this, there was a 175 day drought that was likely causing dehydration so many of the observed rattlesnakes that emerged were coiled up outside the den collecting rainwater and melting snow on their bodies to drink.
Overwintering is a crucial part of the survival of rattlesnakes, especially in the northern portions of their ranges. As mentioned previously, many rattlesnake species have demonstrated high site fidelity to these dens particularly if there is little habitat already available. Plus, if they return to a habitat that is no longer there or so highly altered it is unusable, they will likely not be able to survive the winter unless they can find another location in time. Additionally, habitat fragmentation is just as consequential as rattlesnakes may no longer be able to access their overwintering habitat or die in the process of getting there. Further, a study completed in New York concluded that based on a low genetic diversity in their study areas, timber rattlesnakes that overwintered in fragmented habitat often stayed in these isolated "islands", avoided roads, and were more likely to mate with individuals in the same habitat "island". These areas of low genetic diversity could have large impacts on this rattlesnake species in the region overtime.
The above sample of overwintering behaviors and habitat use is just a single example of why it is so important to work to protect BOTH the rattlesnake species themselves as well as the habitat they live in. The Rattlesnake Conservancy does this in a variety of ways, such as working with local, state, and federal agencies to establish legislature to protect rattlesnakes and the land they live on as well as supporting researchers like our most recent grant recipient project studying the Northeastern rattlesnake in Brazil. Help us accomplish our mission to protect rattlesnakes and their habitat by becoming a member today!