A Preliminary Assessment of Mouflon Abundance at the Kahuku Unit of Hawaii Volcanoes National Park

Department of the Interior

U.S. Geological Survey

Open-File Report 2006-1193


By Steven C. Hess, Ben Kawakami Jr., David Okita, and Keola Medeiros


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Hawaii Volcanoes National Park (HAVO) recently acquired the 115,653 acre Kahuku Ranch unit adjacent to the existing Mauna Loa section of HAVO. Kahuku contains numerous exceptional natural resources including many federally listed threatened and endangered species. An apparently large and growing population of alien mouflon sheep (Ovis gmelini musimon), however, threatens sensitive native plants and forest bird habitats. Population composition and abundance estimates were urgently needed to determine the magnitude of resources required to manage this species and justify costs. We surveyed 32,433 acres from helicopter over 2 days in November 2004 during breeding to determine the abundance and population structure. We estimated that there were more than 2,586 ± 705 (90% CI) mouflon at Kahuku. Overall, group sizes averaged 7.8 and the sex ratio was 1:2.4 rams:ewes, but approximately 44% of the population was concentrated in forested areas near ranching operations where group sizes averaged >15 and the sex ratio was 1:3.9 rams:ewes. The remaining 56% of the population occurred widely dispersed in subalpine shrubland and barren lava flows. Abundance estimates are likely to be conservative because they were not adjusted for detection probability. Ground-based surveys of lambs suggest upper biological limit to annual population increase of 33.1% under existing environmental conditions. Historical information used to calculate population trends indicated the apparent rate of population increase to be 21.1%. In the absence of removals, the population increment for 2004-2005, would be more than 546-856, and the population doubling time with these growth rates is 3-4 years.




Study Area


Aerial Survey

Lamb Surveys

Historical Population Trends


Aerial Survey

Lamb Surveys

Historical Population Trends



References Cited

Appendix I. Kahuku Ranch Monthly Report for June & July 1968

Appendix II. Excerpt from Kahuku Ranch Annual Summary of Operations 1968

Appendix III. Kahuku Ranch Monthly Report for August 1974

Appendix IV. Memo to Trustees of Damon Estate dated 17 August 1993

Appendix V. Letter enclosed with O'Gara's (1994) Report to Trustees of the Damon Estate concerning mouflon on the Kahuku Ranch

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Suggested citation:


Hess S., Kawakami, B. Jr., Okita, D., and Medeiros, K., 2006, A Preliminary Assessment of Mouflon Abundance at the Kahuku Unit of Hawaii Volcanoes National Park: U.S. Geological Survey Open File Report 2006-1193, 22 p.


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