Rattlesnakes in Colorado undergo a period of winter inactivity known as brumation, distinct from mammal hibernation. During brumation, these cold-blooded reptiles significantly reduce their metabolic activity to survive cold temperatures. Unlike true hibernation, brumation involves a less profound dormancy, allowing snakes to occasionally become active on warmer winter days. This adaptation allows rattlesnakes to endure Colorado’s colder months.
The Annual Brumation Cycle
Rattlesnakes in Colorado typically enter brumation in late fall, around October or November, when temperatures consistently drop below 60° Fahrenheit (15° Celsius). This reduced activity continues through winter, with emergence in spring, generally late March or April, as temperatures rise. Timing varies based on local climate and elevation.
During brumation, a rattlesnake’s metabolic rate can decrease by nearly 70 percent, allowing them to survive with minimal or no food. Unlike hibernating mammals, brumating snakes are lethargic but not entirely asleep. They may rouse to seek water or bask in the sun near their den entrance on mild winter days. This allows them to maintain physiological functions and prepare for reproduction upon emergence.
Rattlesnake Brumation Dens
For brumation, rattlesnakes seek sheltered locations called hibernacula, crucial for survival during cold periods. These dens provide protection from freezing temperatures and predators, reducing water loss and conserving energy. Common den types include rock crevices, fissures in rocky outcrops, and abandoned burrows created by other animals like prairie dogs, prairie voles, or thirteen-lined ground squirrels.
Many rattlesnakes exhibit communal denning, gathering in large numbers, sometimes hundreds or even thousands, at these sites. This communal behavior helps conserve heat and offers mutual protection. These hibernacula are often used year after year, with young snakes sometimes following scent trails of adults to find suitable locations. Different snake species, such as bullsnakes and garter snakes, may also share these dens without conflict.
Environmental Cues for Brumation
Rattlesnakes rely on environmental signals to determine when to enter and exit brumation. The most significant cue for entering brumation is a consistent decrease in ambient temperatures. As weather cools in fall, rattlesnakes sense this change and begin migration towards den sites. This temperature drop triggers a reduction in their activity and metabolic rate.
Other contributing factors include shortening daylight hours (photoperiod), which signals winter’s approach. Reduced food availability as prey becomes less active also prompts snakes to seek shelter. Conversely, rising spring temperatures are the primary cue for rattlesnakes to emerge from brumation sites. These environmental changes collectively guide snakes through their annual cycle of activity and dormancy.