The common perception that iguanas, like bears or groundhogs, enter a deep winter sleep is inaccurate, although the reptiles certainly become inactive during cold weather. As ectotherms, or cold-blooded animals, an iguana’s internal body temperature and activity level are directly regulated by the surrounding environment. When the ambient temperature drops significantly, their metabolism slows down dramatically in a survival response to conserve energy. This natural physiological process allows these tropical creatures to cope with temporary cold snaps, especially in regions outside their native habitat, such as the invasive populations in Florida.
Brumation: The Iguana’s Cold Weather Strategy
Iguanas do not undergo true hibernation; instead, they enter a state known as brumation. Hibernation is a deep, continuous metabolic shutdown seen in mammals, where body temperature and heart rate drop drastically and are maintained by internal regulatory processes. A hibernating mammal typically remains in a deep, unconscious sleep for weeks or months, relying solely on stored fat reserves.
Brumation, conversely, is a temperature-dependent state of dormancy where the reptile’s activity is suppressed by the external cold. The iguana’s metabolic rate slows but does not achieve the profound, sustained drop characteristic of mammalian hibernation. Unlike a true hibernator, a brumating iguana remains somewhat aware of its surroundings and may occasionally wake up to drink water during brief, warmer spells. This ability to rouse distinguishes the reptile’s cold-weather survival strategy from the deep, uninterrupted sleep of a true hibernating mammal.
Environmental and Metabolic Triggers
The primary signal initiating brumation is a consistently low ambient temperature, typically falling below 50°F (10°C). When temperatures drop lower, often into the 40–45°F (4–7°C) range, muscular control can become compromised, leading to near-paralysis. Secondary environmental cues include a decreased photoperiod (shorter daylight hours), which signals the change of season. These external factors work in tandem with internal hormonal changes to trigger the slowdown.
Internally, the iguana’s body begins a physiological shift in preparation for dormancy. The heart rate and respiratory rate decrease substantially, and the digestive process slows to an almost complete stop. Because a reptile cannot properly digest food without sufficient heat, any food remaining in the gut would rot, potentially causing fatal internal infection. Consequently, iguanas must clear their digestive tracts completely before dormancy begins, a process that can take up to two weeks after their last meal.
During brumation, the iguana relies on stored energy reserves to sustain its minimal bodily functions. The slowed metabolism reduces the rate at which these reserves are consumed, allowing the animal to survive for an extended period without eating. This period of inactivity also places a strain on the immune system, which is suppressed, making a healthy body condition essential before the cold period.
Caring for Iguanas During Periods of Dormancy
In the wild, iguanas naturally seek out safe havens, such as burrows, dense foliage, or rock crevices, to shield themselves from the harshest cold. In regions like Florida, where iguanas are an invasive species, sudden and severe cold snaps can lead to the well-known phenomenon of “cold-stunning.” This occurs when the temperature drops below the threshold for muscular control, causing the iguanas to become lethargic and fall from the trees where they roost.
Stunned iguanas are not dead, but they are temporarily immobilized and unable to move until they warm up. Wildlife officials advise the public to leave these stunned animals alone, as they will typically recover their mobility once temperatures rise. Moving a cold-stunned iguana indoors is ill-advised, as the sudden warming can cause stress, and the animal may become active and aggressive once it thaws.
Intentional brumation for pet iguanas is generally unnecessary and risky unless supervised by a reptile veterinarian, as their native tropical environment does not require this survival strategy. Owners should maintain a consistent, warm environmental gradient and a stable light cycle year-round to prevent the natural cues for dormancy. If a pet iguana accidentally experiences a cold snap or shows signs of reduced activity and appetite, avoid feeding it until normal basking temperatures are restored and the animal is fully active again. Hydration is key during any period of reduced activity; providing a shallow dish of fresh water is important, as the iguana may briefly rouse to drink.