Population Characteristics of Feral Sheep on Santa Cruz Island
Van Vuren D and Coblentz BE. 1989. Population Characteristics of Feral Sheep on Santa Cruz Island. The Journal of Wildlife Management. 53(2):306-313
We evaluated population characteristics of feral sheep (Ovis aries) on Santa Cruz Island from 1979 to 1981. Santa Cruz Island supported an estimated 21,240 feral sheep on 22,000 ha; mean densities were as high as 2.1 sheep/ha. Sheep attained adult weight by 2.5 years. Physical condition varied seasonally according to reproductive chronology, with no evidence of emaciation. A young age structure suggested an increasing population, and female-biased sex ratios probably resulted from higher mortality of reproductively active males. Lambing occurred during a 1-month period that coincided with the onset of the growing season; lamb survival was close to 100%. Ninety percent of females were pregnant or lactating, and the percentage of females lactating increased with age, with no decrease among old animals. Many females first conceived when about 7 months old. Home ranges and minimum daily movements varied seasonally in relation to forage availability and timing of the rut. Groups were small, with 80% totaling ≤7 sheep. We concluded that feral sheep were maintaining a healthy population despite habitat degradation due to long-term overgrazing, and recommended that feral sheep be removed from the island. That recommendation was carried out.
- Type
- Journal Article
- Authors
- Van Vuren, Dirk; Coblentz, Bruce
- Units
- CHIS
- Keywords
- Animal Studies, Eradication, Feral Animals, Grazing, Health, Santa Cruz Island Channel Islands National Park CA, Sheep (Domestic)