General Biology, Reproduction, and Behavior
Ground squirrels construct and live in extensive underground burrows, sometimes up to 6 feet (2 m) deep, with many entrances. They also use
and improve on the abandoned burrows of other mammals such as prairie dogs and pocket gophers. Most return to their nests of dried vegetation
within the burrows at night, during the warmest part of summer days, and when they are threatened by predators, such as snakes, coyotes, foxes, weasels, badgers, and raptors. The squirrels generally enter
their burrows to estivate, escaping the late summer heat. They hibernate during the coldest part of the winter. Males usually become active above ground 1 to 2 weeks before the females in the spring, sometimes as early as late February or early March. A few may be active above ground throughout the year.
Breeding takes place immediately after emergence. The young are born after a 4- to 5-week gestation period with 2 to 10 young per litter. Generally only 1 litter is produced each year. Densities of the ground squirrel populations can range from 2 to 20 or more per acre (5 to 50/ha).
Damage Prevention and Control Methods Exclusion
Exclusion is impractical in most cases because ground squirrels are able to dig under or climb over most simple barriers. Structures truly able to exclude them are prohibitively expensive for most situations. Sheet metal collars are sometimes used around tree trunks to prevent damage to the base of the trees or to keep animals from
climbing trees to eat fruit or nut crops.
Cultural Methods/Habitat Modification Flood irrigation of hay and pasture lands and frequent tillage of other crops discourage ground squirrels somewhat. Squirrels, however, usually adapt by building the major part of their burrows at the margins of fields, where they have access to the crop. During the early part of the season they begin foraging from the existing burrow system into the field until their comfort escape zone is exceeded.
When this zone is exceeded and as the litters mature in the colony, tunnels will be extended into the feeding area. Late in the summer or fall, tillage will destroy these tunnels but will not disturb or destroy the original system at the edge of the field. Some research has been conducted on the effect of tall vegetation on ground squirrel populations and movements. The data, while sketchy, indicate that the squirrels may move out of tall vegetation stands to more open grass fields. The addition of raptor (hawk, owl, and kestrel) nest boxes and perches around the field border or throughout the colony may reduce colony growth, but is not a reliable damage control method.