Population Characteristics of Feral Sheep on Santa Cruz Island

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.