Correlates to colonizations of new patches by translocated populations of bighorn sheep

By 1950, bighorn sheep were extirpated from large areas of their range. Mos t extant populations of bighorn sheep (Ovis canadensis) in the Intermountai n West consist of <100 individuals occurring in a fragmented distribution a cross the landscape. Dispersal and successful colonizations of unoccupied h abitat patches has been rarely reported, and, in particular, translocated p opulations have been characterized by limited population growth and limited dispersal rates. Restoration of the species is greatly assisted by dispers al and successful colonization of new patches within a metapopulation struc ture versus the existing scenario of negligible dispersal and fragmented, s mall populations. We investigated the correlates for the rate of colonizati ons 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 N-e of th e founder group, and early contact with a second released population in a n earby release patch (logistic regression, p = 0.08). Largest population siz e of all extant released populations in 1994 was correlated to potential N- e of the founder group, the number of different source populations represen ted 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). S uccessful 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 popula tion (p = 0.05). Fewer water barriers, more open vegetation and more rugged , broken terrain in the intervening habitat were also associated with colon izations (p = (0.05). We concluded that high dispersal rates and rapid reoc cupation of large areas could occur if bighorn sheep are placed in large pa tches of habitat with few barriers to movements to other patches and with n o domestic sheep present. Many restorations in the past that did not meet t hese criteria may have contributed to an insular population structure of bi ghorn sheep with limited observations of dispersal.