Rattlesnakes are ectothermic, meaning their body temperature is regulated by their external environment. They cannot generate their own body heat and rely on their surroundings to stay warm. This reliance means rattlesnakes must adapt to seasonal temperature changes. The dormant state reptiles enter during colder periods is called “brumation,” distinct from the “hibernation” of warm-blooded animals. Reptiles in brumation are in a state of reduced activity where their body temperature fluctuates with the environment, allowing them to survive when temperatures drop and food is scarce.
The Onset of Rattlesnake Brumation
Rattlesnakes typically begin brumation in late fall, often around November. Declining ambient temperatures and decreasing daylight hours are primary environmental cues. When temperatures consistently drop below 60°F (15°C), rattlesnakes become sluggish and seek shelter. Prolonged cold makes it difficult for them to function.
Food scarcity also contributes to brumation. Prey animals become less active, making hunting difficult. Before entering brumation, rattlesnakes may increase their food intake to build up fat reserves, but they stop eating once temperatures fall to avoid undigested food rotting in their systems. The shortening photoperiod also influences hormonal changes that prompt this dormant behavior.
Life During Brumation
During brumation, rattlesnakes undergo physiological changes to conserve energy. Their metabolic rate slows, reducing heart rate and respiration. This allows them to survive for months with minimal or no food, relying on stored fat reserves. While in this state, rattlesnakes are not truly “asleep” in the way mammals hibernate; they remain lethargic but aware of their surroundings and can rouse on warmer days.
Rattlesnakes seek out underground shelters for brumation, known as hibernacula. These sites often include rock crevices, abandoned rodent burrows, caves, or even spaces under porches or sheds. The underground locations provide stable temperatures, protecting them from freezing. Many rattlesnake species exhibit communal denning, gathering in large groups that can range from a few individuals to hundreds, or even over a thousand, in a single den. This communal behavior helps conserve warmth and provides safety from predators, and they often return to the same den year after year.
Waking from Winter Slumber
Rattlesnakes emerge from brumation in the spring, typically from late March through May, depending on the local climate and specific species. The primary environmental triggers for their awakening are rising ambient temperatures and increasing daylight hours. As average ground temperatures consistently reach or exceed about 50°F (10°C), the snakes begin to stir from their dens.
Upon emergence, rattlesnakes are often sluggish and will bask in the sun to warm their bodies to optimal temperatures, which are typically between 85-92°F (29-33°C). This initial warming period is crucial for their physiological processes to return to normal activity levels. While they may briefly emerge on warmer winter days to bask, significant activity, including hunting and mating, resumes as spring progresses. The timing of emergence can be influenced by climate conditions, with warmer springs potentially leading to earlier activity.