These temporary burrows or pallets can be fragile and may be used for shelter for a few days while a tortoise is foraging in a particular area. A temporary burrow usually lasts from a few weeks to a season and then disintegrates. Each tortoise usually has more than one burrow. The number of burrows the tortoise uses depends on age and sex, as well as on the season. The burrow is usually the size and shape of the tortoise - half moon in shape and flat on the bottom.
Small tortoises have small burrows and large tortoises have large burrows.
The tortoise burrow provides protection from the extremes of heat, cold, lack of moisture, and too much moisture. The tortoise spends most of its life in the burrow. Burrows serve as protection from predators, such as common ravens, coyotes, kit foxes, golden eagles, and greater roadrunners. Migration refers to movement to a particular place for a particular purpose, such as feeding or breeding, and then return to the former site. I do not think that migration is an appropriate term to use for tortoise movements.