Brumation
From UroWiki
Brumation is an example of dormancy in reptiles that is similar to hibernation. It differs from hibernation in the metabolic processes involved.
Reptiles generally begin brumation in late autumn, although this can vary considerably from reptile to reptile. They will often wake up to eat and then return to "sleep". They can and do eat during this time, but can go weeks or months without food. Reptiles may want to eat more than usual before the brumation time, but will eat less or refuse food as the temperature drops. However, they do need water intake, which they get only from their greens. For this reason, you should to provide the same amount of greens on the same schedule as before, regardless of whether or not your uromastyx seems to be awake or eating, so that it has a source of fluid intake available when it does reappear.
Length and duration of brumation periods
The brumation period is anywhere from 1-8 months depending on the air temperature and the size, age, and health of the reptile. Observation has shown that uromastyx can be consistently active during the winter for around 6-8 hours per day, or they can sleep for as much as a week at a time, without problems - it varies with each individual, and with the specific conditions of the day.
Uromastyx don't hibernate
Brumation should not be confused with hibernation; when mammals hibernate they are actually asleep, when reptiles brumate they are less active, their metabolism slows down so they just don't need to eat as often. Reptiles can often go through the whole winter without eating. Brumation is triggered by cold weather/lack of heat, and the decrease in the amount of hours of daylight in the winter - however, although informal studies have shown that uromastyx react to changes in light levels, pressure, day length, and external temperature (even when kept away from a window onto the outside world), it is not yet fully known how an artifical environment (such as in a terrarium) affects this behaviour. It is believed that they follow an instinctive biological clock.
