The Influence of Cattle Grazing on California Ground Squirrels in a Blue Oak Savanna1

This experiment compared California ground squirrel (Spermophilus beecheyi) activity on replicated grazed and ungrazed pastures in a blue oak (Quercus douglasii) savanna. During the 4-year study, squirrel activity, measured as the number of active burrows, generally declined in grazed and ungrazed pastures without oak canopy. Squirrel activity declined least in grazed pastures with blue oak canopy, and by the end of the experiment those pastures had significantly highest squirrel activity. Livestock management has only moderate potential for influencing squirrel abundance on grazed blue oak rangeland. The California ground squirrel (Spermophilus beecheyi) is a native rodent common on rangelands (Lidicker 1989). As an agricultural pest on annualdominated range, it damages structures, eats crops, serves as a disease vector, and competes with livestock for forage. As an indigenous component of rangeland ecosystems, ground squirrels are an important prey species and help support a diversity of predators. Studies at the San Joaquin Experimental Range near Fresno suggested that squirrels compete with livestock for forage, and that livestock grazing increases squirrel populations (Howard and others 1959, Fitch and Bentley 1949). Heavy livestock grazing was proposed to reduce litter and favor the germination of broadleaved plants more desirable to squirrels (Howard 1953). Linsdale (1947) observed, at the Hastings Reservation in Carmel Valley, that both light and heavy grazing favored squirrels, presumably through changes in species composition and litter, and that removal of grazing leads to disappearance of squirrels. I compared moderate cattle grazing and grazing removal on replicated pastures in oak savanna and annual grassland at Del Valle Park in southern Alameda County to determine the effects on ground squirrel abundance.