Ground Squirrel

GROUND SQUIRREL, belongs to the rodents (see), family Sciuridae. A small animal, up to 40 cm in length (large species) and up to 25 cm (small species). Inhabits North America, Europe, and Asia. The most important species found in the USSR belong to the genus Citellus (in previous literature Spermophilus): C. citellus - in western Ukraine, C. suslica - the spotted ground squirrel, between the Volga and Dnieper, C. pygmaeus - from the Dnieper to the Altai (fig. 1), one of the most important carriers of plague (subspecies musicus, mugozaricus and others), C. dauricus - Transbaikalia, C. fulvus - large yellow, or sandy ground squirrel - from the Volga to Central Asia. C. rufescens - a large species, between the Volga and Urals, C. eversmanni - long-tailed Siberian, closer to the squirrel and North American species. The genus Spermophilopsis is found in the sandy deserts of Central Asia (Sp. leptodactylus - thin-toed ground squirrel). In North America, ground squirrels, called there ground squirrels, prairie dogs, are represented by the genera Citellus and Cynomys. Ground squirrels live in burrows dug in hard ground and having a depth of 1-2 m. The structure of burrows is varied. Usually there is an inclined passage forming several "knees" and side passages and ending in a nesting chamber, as well as a vertical "straight up" passage; the ground squirrel begins to dig it from the inside, preparing for winter, and blocks the inclined passage with the dug-up earth, making a "plug". In spring the vertical passage is extended to the surface and the ground squirrel emerges through it (fig. 2). In a burrow lives no more than one ^A

young animal, but burrows are located close to each other and form colonies. On 1 hectare on average there are 100-200 burrows of small ground squirrels (rarely up to 1,500), and in large species no more than 30-50 burrows. Each ground squirrel uses several burrows and the actual number of ground squirrels on each hectare is from 5% to 20% of the number of existing burrows. Ground squirrels feed on plant food and only occasionally on insects and the like. During the absence of food (drying up of the steppe, winter) they fall into hibernation lasting up to 7 months. Hibernation is accompanied by numbness, lowering of body temperature (to +1°), breathing becomes rare and even stops, heartbeat occurs 1-2 times per minute. Life processes occur due to existing fat reserves. In spring ground squirrels awaken, come to the surface and mate. Pregnancy lasts 23-25 days. 3 to 11 young are born. Old ground squirrels, having accumulated fat reserves, go into hibernation already in June-July, males earlier than females, young ones in September, and the long-tailed Eversmann's ground squirrels remain active almost until snowfall. A month after birth, young ground squirrels disperse from burrow to burrow in search of food; during this period optimal conditions are created for the development of epizootics among them due to contact with other ground squirrels and infected burrows. The movements made by ground squirrels are usually small (within 10-100 m). Experiments with banding small ground squirrels, C. pygmaeus and others showed that the maximum movement in a year does not exceed 5 km. When settling, for example, in the Stavropol steppes, ground squirrels in 12 years moved only 45-75 km. More mobile are C. eversmanni - up to 180 km per year, they cross rivers. Mortality of ground squirrels is high. By banding C. pygmaeus in the North Caucasus it was established that to the next year 31% survive, to 2 years - 10%, to 3 years and above - 0.7%. The cause of high mortality are natural enemies - predatory birds, ferrets, which are therefore subject to protection, and epizootics. The greatest importance are epizootics of plague (see). Epizootics among ground squirrels are established most easily by collecting carcasses in the steppe (in a chain of investigators) and bacteriological examination of them, and sometimes several carcasses are found per 1 hectare. Examination of live ground squirrels caught by pouring water into burrows or with traps also sometimes allows finding up to 10-15% infected with plague. Infection of people from ground squirrels occurs through contact with them (skinning, preparation for food, children's play, guarding crops, shepherds, bringing carcasses by domestic animals, etc.), as well as through ectoparasites that pass to humans; ground squirrel fleas - Caratophyllus tesquorum, Neopsylla setosa and others - can bite humans. For economic purposes, skins are purchased (C. fulvus is valuable), fat is used for technical purposes; ground squirrel meat is edible. In a plague-infested area, ground squirrel hunting is prohibited during the epizootic period. It is possible to use ground squirrels as laboratory animals for experiments with plague, tularemia, brucellosis, typhus, cholera (young) and other infections. Control of ground squirrels as agricultural pests and carriers of plague is carried out by methods described in deratization (see). To combat plague and protect crops, partial cleanings of areas from ground squirrels near populated areas and crops (zone 1-5 km) are often carried out; these works have temporary significance, since in 1-2 years the area is re-populated. Continuous radical cleanings of large areas from ground squirrels have so far given little success due to technical difficulties. In the USSR this task is now being resolved with the help of repeated cleanings from year to year, carried out by OB.

Figure 1. Young ground squirrels (Citellus pygmaeus Pall.).

Figure 2. Diagram of temporary (A) and permanent (B) burrows of a ground squirrel.