Garter snakes, common reptiles found across North America, employ a survival strategy known as brumation to endure the colder months. This state of inactivity, often compared to mammal hibernation, allows them to survive low temperatures and limited food. Unlike true hibernation where animals enter a deep sleep and primarily rely on fat reserves, brumating reptiles remain somewhat aware and responsive to their surroundings. This adaptation aids their survival.
When Garter Snakes Begin Brumation
Garter snakes typically begin their brumation period in late fall to early winter. Timing varies by geographical location, occurring earlier in northern regions and later or not at all in warmer southern climates. For instance, in many areas, they seek shelter between September and early November.
Environmental cues, such as consistent drops in ambient temperature, trigger this transition. When temperatures fall below approximately 16°C (60°F), garter snakes start seeking suitable overwintering sites. Decreasing daylight hours also signal the approaching cold season. Before entering brumation, snakes stop eating for several weeks to ensure their digestive systems are completely empty, preventing food from rotting within their bodies during inactivity.
The Spring Emergence
Garter snakes emerge from their brumation dens from early to mid-spring. Rising ambient temperatures, often consistently above 15°C (59°F), are the primary environmental signal that prompts them to become active again. Increasing daylight also plays a role in this seasonal transition.
Male garter snakes often emerge slightly earlier than females from the communal dens. They gather near the den entrances, awaiting the females. Once females appear, mating activities begin almost immediately, as brumation is important for stimulating reproductive behaviors.
Choosing a Brumation Den
The locations garter snakes choose for brumation are known as hibernacula. These dens offer protection from freezing temperatures and predators during their vulnerable state. Common types of hibernacula include natural rock crevices, abandoned burrows made by other animals like rodents or crayfish, and even man-made structures such as building foundations, steps, or stone walls.
These dens must extend below the frost line, which can be more than a meter deep in some areas. This depth ensures that temperatures within the hibernaculum remain stable and above freezing, typically between 3-6°C (37-43°F), preventing the snakes from succumbing to the cold. Garter snakes often hibernate communally, with dozens to thousands of individuals gathering in a single den, which helps them conserve body heat and increases their collective survival chances.
Surviving the Winter Sleep
During brumation, garter snakes undergo physiological adaptations to survive the prolonged period of inactivity. Their metabolism slows dramatically, leading to a reduced heart rate and respiration. For instance, oxygen consumption can decrease by over 50%, and cardiac activity may be depressed by more than 75%. Their body temperature generally matches the ambient temperature of the hibernaculum, which remains just above freezing.
Garter snakes rely on stored energy reserves, primarily from fat and glycogen accumulated during warmer months, to sustain themselves throughout this period. They do not consume food or excrete waste while in brumation. Although their activity is minimal, they are not in a deep sleep like hibernating mammals; they remain sluggishly awake and can move within the den. On particularly mild winter days, it is possible for them to emerge briefly to bask in the sun before retreating back into their underground shelters.