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By 1950, bighorn sheep were extirpated from large areas of their range. Most extant populations of bighorn sheep (Ovis canadensis) in the Intermountain West consist of <100 individuals occurring in a fragmented distribution across the landscape. Dispersal and successful colonizations of unoccupied habitat patches has been rarely reported, and, in particular, translocated populations have been characterized by limited population growth and limited dispersal rates. Restoration of the species is greatly assisted by dispersal and successful colonization of new patches within a metapopulation structure versus the existing scenario of negligible dispersal and fragmented, small populations. We investigated the correlates for the rate of colonizations of 79 suitable, but unoccupied, patches by 31 translocated populations of bighorn sheep released into nearby patches of habitat. Population growth rates of bighorn sheep in the release patches were correlated to Ne of the founder group, and early contact with a second released population in a nearby release patch (logistic regression, p = 0.08). Largest population size of all extant released populations in 1994 was correlated to potential Ne of the founder group, the number of different source populations represented in the founder, and early contact with a second released population (p = 0.016). Dispersal rates were 100% higher in rams than ewes (p = 0.001). Successful colonizations of unoccupied patches (n = 24 of 79 were colonized) were associated with rapid growth rates in the released population, years since release, larger area of suitable habitat in the release patch, larger population sizes, and a seasonal migratory tendency in the released population (p = 0.05). Fewer water barriers, more open vegetation and more rugged, broken terrain in the intervening habitat were also associated with colonizations (p = <0.05). We concluded that high dispersal rates and rapid reoccupation of large areas could occur if bighorn sheep are placed in large patches of habitat with few barriers to movements to other patches and with no domestic sheep present. Many restorations in the past that did not meet these criteria may have contributed to an insular population structure of bighorn sheep with limited observations of dispersal.

Desert Bighorn Climate Change Vulnerability populations occupying relatively intact landscapes, such as Death Valley and Grand Canyon national parks, had the lowest overall vulnerability. These results provide local and regional context for conservation and management decisions regarding bighorn populations in a changing climate. Our study further demonstrates how assessments combining multiple factors could allow a more integrated response, such as increasing efforts to maintain connectivity and thus potential for adaptation in areas experiencing rapid climate change.

ContextHuman activity in wildlands can influence wildlife populations by decreasing or degrading habitat, decreasing survival, or through displacement. For bighorn sheep (Ovis canadensis), some human activities are detrimental and may result in physiological stress, altered activity budgets, or habitat abandonment. From 1979 to 2000, human recreation increased over 300% in areas occupied by desert bighorn sheep (O. c. nelsoni) in south-eastern Utah. Concurrently, the population of desert bighorn sheep occupying the Potash Bighorn Sheep Management Unit of south-eastern Utah was in steep decline. AimsWe investigated behavioural responses of desert bighorn sheep to different levels of human activity in this area from 2002 to 2003. MethodsWe divided the study population into two areas on the basis of the level of human use, i.e. low and high. We observed desert bighorn sheep at seven sites within these areas, including three with a high level of human use and four areas of a low level of human use. Key resultsDesert bighorn sheep spent significantly less time grazing and more time vigilant in areas of a high level of human use than in areas of a low level of human use. ConclusionsHuman recreational use of desert bighorn sheep habitat has the potential to negatively affect foraging by desert bighorn sheep. ImplicationsWe raise a cautionary flag because recreational use in bighorn sheep habitat near Moab, Utah, continues to increase and bighorn numbers continue to decline. When managers consider proposals to increase areas or trails for human recreation, they should incorporate ways to minimise impacts and reduce stressors to bighorn sheep.

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