A Short Season and Its Effect Upon the Preparation for Reproduction by the Columbian Ground Squirrel

Abstract

Seasonal Condition of the Columbian Ground Squirrel The season of active life of the Columbian ground squirrel (Citellus colunibianus columibianus) at Pullman in southeastern Washington is but little over five months. All the rest of its yearly life is spent in aestivation and hibernation. This very short period of activity, a result of peculiar climatic conditions, makes necessary the proper preparation by nature for the period of prompt breeding and early development of the young. This preparation manifests itself at least in two ways: First, in the accumulation of sufficient body fat to carry the animals not only through the adverse period of aestivation and hibernation but also past the very exacting period of subsequent breeding and rearing of the young. Second, in the restoring of the activities of the genital organs, to such a degree that it is possible for reproduction to commence almost at once after the animal's return hibernation. It is popularly supposed that an awakening squirrel on appearing again after its long sleep is emaciated and quite destitute of body fat. Such is not the case as is seen in Plate VII, i, representing a squirrel immediately after returning from six or seven months of torpor. At the time of retiring to aestivation these animals are enormously fat (P1. VII, 3), and though this reserve supply is drawn upon constantly during the long months of inactivity (PI. VII, 4) yet at the time of awakening (PI. VII, 2) they are still remarkably fat. It is not until the sequence of mating, gestation, birth, nourishing and weaning of the young have all taken place that the reserve fat accumulated the previous summer has been largely drawn upon. This is a useful provision to meet a peculiar demand; for the species is a non-drinker of water, and must cease activity when the season of drought settles down; for the moisture element of its food comes from succulent plants, hence the short period of active life.