"Expensive management efforts to restore or increase bighorn sheep populations should focus on large habitat patches," say Francis Singer of the U.S. Geological Survey at Colorado State University in Fort Collins and his co-authors in the October issue of Conservation Biology.

Singer and his colleagues determined whether the persistence and growth rate of 24 translocated bighorn sheep populations in Colorado correlated with a variety of factors, including population size, habitat size and quality, ability to migrate, and distance from domestic sheep, which can spread disease to bighorns.

While a number of factors correlated with bighorn persistence, the researchers concluded that the primary factor is habitat size and quality. The small patches in the study averaged 32 square miles, and the large patches averaged 61 square miles. Larger patches have more high quality forage, provide more opportunities to migrate and presumably make it easier to avoid predators. The researchers also found that the populations in larger patches increased faster and were more likely to colonize other habitat patches.

Singer and his colleagues recommend that costly efforts to restore bighorns -- such as creating habitat corridors and water sources -- should focus on populations in large habitat patches rather than on those in small, isolated patches.

While smaller patches generally have smaller populations, the researchers caution that "not all small populations should be written off." Small patches of high-quality habitat could also warrant restoration efforts.

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Contact: Francis Singer
francis@nrel.colostate.edu
970-491-7056
Society for Conservation Biology
20-Sep-2001