Distribution and abundance of bighorn sheep in the Peninsular Ranges, California

E. S. Rubin, Walter M Boyce, M. C. Jorgensen, S. G. Torres, C. L. Hayes, C. S. O'Brien, D. A Jessup

Research output: Contribution to journalArticle

42 Scopus citations

Abstract

We examined the current population structure and past trends in abundance of endangered bighorn sheep (Ovis canadensis) in the Peninsular Ranges of California using a variety of approaches. Direct observations of radiocollared animals (N = 90 ewes and 24 rams) during 35 months suggested that bighorn distribution in the Peninsular Ranges was fragmented into ≥8 groups of ewes. These findings were supported by aerial-telemetry locations of radiocollared ewes obtained during 43 fixed-wing flights and observations of uncollared bighorn sheep made during 2 helicopter surveys. Boundaries between ewe groups coincided, in 4 cases, with paved roads, leading us to speculate that some fragmentation was recent and artificial. Abundance estimates derived for 5 of the 8 ewe groups in 1994 and 1996 revealed a recent decline of 28% in this portion of the range. Adult population estimates were generated and combined with existing estimates for the remainder of the range to produce estimates of 347 and 276 bighorn sheep in the Peninsular Ranges north of the United States-Mexico border in 1994 and 1996, respectively. Linear regression analysis of 26 years of waterhole count data, collected at 30 sites representing regions used by 4 ewe groups, indicated that numbers of ewes had declined in 2 of these regions since 1971, but that 2 regions had been inhabited by stable ewe populations during this period. We suggest that groups of bighorn sheep in different portions of the Peninsular Ranges are under local influences and exhibit independent population dynamics.

Original languageEnglish (US)
Pages (from-to)539-551
Number of pages13
JournalWildlife Society Bulletin
Volume26
Issue number3
StatePublished - 1998

Keywords

  • Bighorn sheep
  • California
  • Distribution
  • Ovis canadensis
  • Peninsular Ranges
  • Population fragmentation
  • Population trends

ASJC Scopus subject areas

  • Animal Science and Zoology
  • Ecology

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    Rubin, E. S., Boyce, W. M., Jorgensen, M. C., Torres, S. G., Hayes, C. L., O'Brien, C. S., & A Jessup, D. (1998). Distribution and abundance of bighorn sheep in the Peninsular Ranges, California. Wildlife Society Bulletin, 26(3), 539-551.