Rattlesnakes are ectothermic, meaning their body temperature is regulated by their external environment. Unlike mammals, rattlesnakes depend on surrounding temperatures to maintain physiological functions. This reliance on environmental conditions makes temperature a significant factor for their survival, activity, and well-being.
Temperature for Inactivity and Survival
When ambient temperatures drop below 60°F (15°C), rattlesnakes typically become less active, displaying sluggish behavior. They can still move at temperatures above freezing, but it is uncommon to see them active below 65°F (18°C), and very rare below 55°F (13°C). Even when sluggish, a rattlesnake remains capable of striking quickly if provoked, as long as temperatures stay above freezing.
The critical lower limit for their survival without adequate shelter is generally around 40°F (4-5°C). While they can endure brief exposures to temperatures as low as 4°F (-16°C) and survive for several days at 37°F (3°C) in protected spaces, prolonged exposure to freezing temperatures (below 32°F/0°C) without insulation can be lethal, leading to cellular damage and freezing. Rattlesnakes prefer a much warmer range of 70-90°F (21-32°C) for optimal activity, and their digestive processes are most efficient when their body temperature is between 80-85°F (27-29°C).
The Brumation Process
When temperatures consistently fall below their active range, rattlesnakes enter a state known as brumation. This physiological process is similar to hibernation in mammals but differs as brumating reptiles are not in a deep, continuous sleep. During brumation, a rattlesnake’s metabolism slows considerably, sometimes by nearly 70 percent, allowing them to conserve energy and survive cold weather and food scarcity by relying on fat reserves.
Before brumation, rattlesnakes typically cease feeding because their digestive system requires warmth to function properly. Undigested food remaining in their system when temperatures drop could rot and become harmful. While brumating, rattlesnakes remain lethargic, but they may occasionally emerge on warmer winter days to bask or seek water before returning to shelter. This dormant state also triggers hormonal changes necessary for spring breeding readiness.
Where Rattlesnakes Seek Shelter
To survive cold temperatures, rattlesnakes seek specific sheltered locations known as hibernacula. These dens are often communal, with multiple snakes gathering, sometimes numbering in the hundreds or even over a thousand. Common hibernacula sites include rocky crevices, abandoned burrows dug by other animals like prairie dogs, natural caves, or spaces under rock piles and human-made structures such as porches or sheds.
These dens provide insulation from freezing temperatures, often extending below the frost line. Many rattlesnake species return to the same den year after year. These communal retreats can also be shared with other snake species or animals, serving as crucial overwintering habitats. Hibernacula are frequently found on south, southeast, or southwest-facing slopes, which allows for greater solar exposure and slightly warmer microclimates.