As temperatures drop and daylight wanes, snakes, being cold-blooded, must employ strategies to survive colder months. Unlike warm-blooded creatures that internally regulate body temperature, snakes rely on their external environment. This reliance necessitates unique behavioral and physiological adaptations to endure cold, ensuring their survival until warmer conditions return.
The Winter State: Brumation
Snakes enter brumation, a state distinct from mammal hibernation. While both involve dormancy, brumation is a less profound inactivity.
During brumation, a snake’s metabolism slows significantly. Its heart rate can drop to 5-10 beats per minute from a typical 60-80, and breathing reduces from dozens per minute to just 6-10 per hour.
Unlike true hibernators, brumating snakes do not enter continuous deep sleep. They remain somewhat alert and can move around. On mild winter days, they may emerge to bask in the sun, though they do not venture far. This state conserves energy without relying on stored fat, as metabolic needs are greatly reduced. They do not eat during brumation because their digestive system shuts down, and food would rot internally.
Finding Winter Shelter: Hibernacula
To survive cold, snakes seek winter shelters called hibernacula. These underground chambers protect them from freezing. A suitable hibernaculum must maintain a consistent temperature above 0°C (32°F) and be located below the frost line, typically over 1 meter (3 feet) deep. The site also needs stable humidity to prevent dehydration, as snakes still require water during brumation.
Hibernacula include natural features like abandoned burrows, rock crevices, caves, decaying logs, or ant mounds. They can also be human-made structures such as old wells, building foundations, or rock piles. Some species brumate alone, while others, like garter snakes, congregate in groups of hundreds or thousands, sometimes sharing dens with multiple species. This communal brumation helps conserve heat and ensures mates are nearby when spring arrives.
Preparing for the Cold
Snakes begin preparing for brumation before winter. As autumn approaches and temperatures decline, they become more active, increasing food intake to build energy reserves. This increased feeding helps them accumulate glycogen, a sugar stored in their bodies, serving as an energy source during inactivity.
As daylight shortens and temperatures consistently drop, snakes search for suitable hibernacula. They may travel long distances to reach these overwintering sites, frequently returning to the same locations year after year. Before entering brumation, snakes clear their digestive tracts to prevent undigested food from decaying, which would be fatal.
Awakening in Spring
When winter recedes and temperatures rise, usually in March or April, snakes emerge from brumation. Consistent environmental warming, often reaching around 15°C (59°F), signals the end of their dormant period. Early spring emergences can see snakes basking near their hibernacula, ready to retreat if temperatures drop again.
Upon emergence, snakes are sluggish as their body temperatures gradually increase from basking. This period marks a return to activity, including foraging for food, as metabolic rates increase. Soon after, many species enter their mating season, completing their annual cycle.