Lizards, like all reptiles, are ectotherms, meaning their internal body temperature is regulated by the surrounding environment. When the weather is warm, they bask in the sun to raise their temperature and become active. When temperatures drop, however, their body functions slow down dramatically. This reliance on external heat sources makes winter survival a challenge in temperate regions, leading to a state of dormancy that conserves energy until spring.
The Process of Brumation
Brumation is the winter dormancy observed in lizards, differing physiologically from the true hibernation of mammals. Unlike hibernating mammals, which regulate their body temperature, the lizard’s temperature simply mirrors that of its shelter. Brumation triggers a reduction in the lizard’s metabolic rate, heart rate, and respiration, slowing down bodily functions to minimize energy expenditure.
During this period, the lizard relies entirely on stored fat reserves, often in the tail, to sustain basic life functions. Brumation is not a continuous, deep sleep; lizards may occasionally rouse to drink water. They do not eat because their digestive system is too slow to process food in the cold. The duration of this torpor varies widely, lasting from a few weeks to several months, depending on the species and the local winter climate.
Selecting the Winter Shelter
When preparing for winter, the lizard seeks a location that offers stable temperatures and protection from freezing. This winter shelter, known as a hibernaculum, must be deep or insulated enough to remain above the frost line, where temperatures can be lethal. The site also needs moisture control, as excessive wetness can cause fungal infections, and excessive dryness can cause fatal dehydration.
Lizards seek out a variety of secure, underground, or heavily covered natural structures for brumation. These sites include deep rock crevices, spaces beneath large, flat stones, and the root systems of trees. Some species actively dig their own burrows, while others utilize tunnels created by rodents or settle deep within decaying logs or compost heaps.
Triggers and Timing
The decision of when to enter brumation is based on environmental cues that signal the impending arrival of winter. The primary external factors that trigger this shift are the sustained drop in ambient air temperature and a change in the photoperiod, or the duration of daylight hours. As the days shorten in late fall, the decreasing light intensity signals the lizard’s internal clock that it is time to slow down and seek shelter.
These cues lead to a behavioral change where the lizard stops feeding and begins searching for a suitable overwintering spot. The timing for emerging from brumation is similarly dictated by the environment. Emergence occurs when sustained warmer temperatures and longer daylight hours return in the spring, signaling the lizard to leave its shelter and resume activity.