Salamanders, like all amphibians, are ectotherms; their internal body temperature is regulated by the surrounding environment. When temperatures drop, they enter a state of winter dormancy to survive harsh conditions. This period of inactivity is often mistakenly called hibernation, but the precise biological term is brumation. The difference between these two forms of dormancy is rooted in the physiology of warm-blooded versus cold-blooded animals.
The Difference Between Hibernation and Brumation
Hibernation is a survival mechanism employed by endotherms, or warm-blooded animals like mammals. A true hibernator dramatically lowers its internal body temperature, heart rate, and respiration into a deep, continuous sleep lasting months. Metabolism slows profoundly, relying primarily on large fat reserves accumulated in the autumn for sustenance.
Brumation is the corresponding state of dormancy for ectotherms, including salamanders, frogs, and reptiles. A salamander’s body temperature closely matches the temperature of its immediate environment. Metabolism slows significantly to conserve energy, but the decrease is not as deep or continuous as in mammalian hibernation.
Brumating animals are not in a continuous, deep sleep. They often wake up sporadically during warmer spells to move or seek out water and rehydrate. This periodic activity is necessary because amphibians are highly susceptible to desiccation. Unlike hibernating mammals, this requirement for intermittent waking and hydration is a major distinction of brumation.
How Salamanders Enter and Maintain Dormancy
The primary environmental cues that trigger brumation are dropping ambient temperatures and reduced daylight hours (the photoperiod). As the temperature falls, the salamander’s physiological processes naturally slow down because their body temperature is externally determined. This reduction in activity allows them to survive for extended periods without feeding.
The metabolic slowdown is coupled with a reduced heart rate and minimal energy consumption. While some energy is derived from fat reserves, amphibians often utilize stored glycogen for energy during brumation, which allows them to function on a lower oxygen supply than mammals. Maintaining proper hydration is a constant struggle, as their permeable skin can lose moisture even in a dormant state.
To manage water loss, salamanders rely on behavioral adjustments, such as finding moist environments. Brumation is also important for reproductive cycles, as the cooling period is necessary for the maturation of sperm and eggs. A salamander will stop eating completely before entering brumation to ensure its digestive tract is empty. This prevents undigested food from decaying and causing illness at low temperatures.
Where Salamanders Spend the Dormancy Period
To successfully brumate, salamanders must locate a spot that offers stable temperatures above freezing and protection from moisture loss. Terrestrial species commonly migrate to underground burrows, often utilizing tunnels created by rodents. These burrows must extend below the frost line; for example, the Tiger Salamander may dig down approximately 60 centimeters to find stable conditions.
Other common winter shelters include the areas beneath large, decaying logs, deep within rock crevices, or under substantial piles of leaf litter on the forest floor. For a species like the Eastern Red-backed Salamander, which is not freeze-tolerant, they may travel as much as 15 inches into the soil to find a secure spot.
Aquatic salamander species, or those that spend part of their time in water, may overwinter submerged. They often burrow into the soft mud or debris at the bottom of ponds or streams. This water-based location is chosen because the water underneath a layer of ice remains above the freezing point, offering a constant, moist, and secure environment.