Anoles, common throughout the southeastern United States, do not hibernate in the traditional sense; they enter a state called brumation. This distinction is important because the physiological processes that occur in reptiles are fundamentally different from those in hibernating mammals. Anoles, such as the green anole (Anolis carolinensis), utilize this seasonal dormancy to survive the colder winter months when their ectothermic bodies cannot function optimally.
Understanding Brumation Versus Hibernation
Brumation and hibernation are both survival strategies, but they reflect the distinct physiologies of the animals that use them. Hibernation is a deep, involuntary state primarily observed in endothermic mammals, such as bears or bats, who regulate their own body heat. During true hibernation, a mammal’s core body temperature drops drastically, and its metabolism slows to a near standstill for weeks or months. This deep sleep relies almost entirely on stored body fat for energy.
Brumation is the corresponding state for ectothermic animals like anoles, whose body temperature is regulated by the external environment. When a reptile brumates, its metabolic rate decreases significantly, but the animal remains somewhat aware of its surroundings. Anoles periodically wake, especially on warmer days, to move or drink water. This periodic activity is necessary to maintain hydration, as reptiles require water to support kidney function during the dormant period.
The Anole’s Seasonal Behavior
The process of brumation for anoles typically begins in late autumn and lasts through the winter, corresponding to the season of reduced light and colder temperatures. As their metabolic rate slows, anoles cease feeding because they are unable to digest food properly without adequate external heat. Undigested food can remain in the gut and rot, which is a lethal condition, so the lizard stops eating entirely before seeking shelter.
Anoles seek sheltered locations to serve as a hibernaculum, which is a general term for a winter retreat. These can be shallow burrows, crevices under rocks, loose bark on trees, fallen logs, or protected spaces inside wall voids of buildings. They become sluggish during this time and may change to a duller brown color, which is often a stress response to the cold.
It is common to find multiple anoles clustered together in a single protected spot during brumation. This collective behavior is driven by the availability of a prime, safe location, as their usual territorial aggression is suppressed by the cold. Anoles remain in this state of reduced activity until the environmental cues of spring signal it is safe to emerge.
Environmental Triggers for Dormancy
The primary factor compelling anoles to enter brumation is a sustained drop in ambient temperature. While anoles can tolerate brief cold snaps, a prolonged period where temperatures consistently fall below a certain threshold triggers the physiological slowdown. For anoles, this threshold is when daytime temperatures drop into the 60 to 70 degrees Fahrenheit range, and nighttime temperatures fall to 60 degrees Fahrenheit or lower.
Decreasing photoperiod, or the shortening of daylight hours, also plays a secondary role as an environmental cue for the onset of brumation. This reduction in available light signals the coming winter and prompts the anole to begin preparing its body by ceasing to feed and seeking out a safe, insulated location. The opposite cues—increasing temperatures, longer days, and higher barometric pressure—signal the end of brumation and the start of the active season in the spring.