<p>The increments on the surface of the incisors of young spotted ground squirrels are wide, of medium clarity. They probably reflect intensive nutrition and growth of the body. Starting with the third month of life, the growth slows down, the width of the increments is decreased, and they become narrower and more distinct. Deformations appear in the form of swellings of the incisor wall. The frequency of occurrence of the deformations in yearlings reaches a peak in the second half of July. The same pattern is observed in adult ground squirrels. By this time, ground squirrels reach their maximum body weight. The majority of adult ground squirrels kept in captivity also reach the maximum body weight in the first half of July, thus indirectly indicating the relationship between the appearance of deformations and the achievement of maximum fatness. Under laboratory conditions, at a temperature below 22°C, after reaching the maximum body weight, overwintered males and dry females fall into a stupor resembling a state of hibernation even in the presence of food. Their body temperature is only 1–1.5°C higher than the room temperature, the animals are lethargic, they do not open their eyes during manipulations, and the frequency of breaths is 4–6 per min. These observations suggest that ground squirrels living in natural conditions also fall into a similar hibernation, since the proportion of overwintered males and females among the individuals caught in the middle of summer is decreased. The appearance of deformations at this time seems to be associated with a violation of the normal growth of the incisors during physiological changes in the body, these being caused by the onset of a transition from the active nutrition of plant food to endogenous consumption of fat reserves characteristic of the state of hibernation. The record of autumn–winter hibernation is characterized by very narrow increments or deformations, a change in the enamel boundary, as well as a change in the contour of the incisor surface. After spring awakening, increments are at first narrow and distinct, 150–160 µm each, subsequently increasing in width, which is probably due to a gradual transition from endogenous nutrition of the body with fat deposits during hibernation to intensive nutrition of green vegetation. Lactation of females usually does not affect daily gains </p>