Is estivation only done to combat weather?
There is direct correlation between estivation and reduced moisture in the environment. There is a tendency in an individual for phases of estivation to alternate with phases of activity. Even under approximately constant external conditions some of the animals would be in either phase. The reason for estivation is a low water content, and that the latter may be brought about either by dryness of the environment or else by the natural hydration cycle of the animals.
