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Population Characteristics of Feral Sheep on Santa Cruz Island
Dirk Van Vuren and Bruce E. Coblentz
The Journal of Wildlife Management
Vol. 53, No. 2 (Apr., 1989), pp. 306-313
Stable URL: http://www.jstor.org/stable/3801128
Page Count: 8
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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.
The Journal of Wildlife Management © 1989 Wiley