The Biology of the Golden‐Mantled Ground Squirrel, Citellus lateralis

Abstract

Citellus lateralis is a rodent of the open coniferous forests of western United States and southwestern Canada. Population density in the various forest types was correlated with density of herbaceous vegetation. It breeds once in early spring and produces an average of 5.1 embryos per litter. The gestation period is approximately 28 days. Young gained approximately 1.2 gm per day while they were nursing, and 3.7 gm per day from the time they began to eat solid food until they were 80 days old. Their eyes opened at 27-31 days of age. The use of eye lenses to determine age was a questionable technique for this species. After the breeding season the reproductive organs involuted rapidly and, after a period of quiescence during the summer, began redeveloping in the fall. Development was greatly accelerated in February. Fungi and leaves constituted 87% of the diet, with seed, flowers, bulbs, fruit, and flesh making up the remainder. The diversified diet enabled the squirrels to remain active except when the ground was frozen or covered with a snow pack. No wild squirrel was observed storing food, and only one of 44 captives made any attempt to store food. Atrophy of the endocrine glands in the fall, a phenomenon common to most hibernators, decreased the metabolic rate and permitted accumulation of fat. Hibernation caused a further reduction in metabolism and enabled the animals to live approximately four months on the accumulated fat. Periodic awakenings were characteristic during the hibernating period; and during open winters, some squirrels came above ground when they awakened. Few animals consumed food from the time they entered hibernation until they awakened in the spring. During hibernation, the submaxillary glands and the digestive tract atrophied and certain histochemical changes were evident. It is suggested that seasonal variation in the endocrine glands, reproductive organs, and other physiological phenomena and behavioral patterns of Citellus lateralis are part of an inherent rhythm which has been modified by selective forces to be compatible with prevalent environmental factors. The stimulus which triggers the various changes and/or the means by which the rhythm is regulated are unknown for this or any other hibernating species.