Compensatory Reproduction in an Introduced Mountain Goat Population in the Absaroka Mountains, Montana

Abstract

Data on reproduction, population trends, and harvest of mountain goats (Oreamnos americanus) in the Absaroka Mountains, southwestern Montana, were analyzed for the period from 1956, when the goats were introduced, to 1983. Kid:older goat ratios were correlated with density of older goats (P < 0.01) and, to a lesser degree, with spring snow depths (P < 0.10). Population trend was best correlated with harvest rate (P < 0.05), but was also negatively correlated with goat density (P < 0.10). Data on hunter success and sex of harvest could not be used to determine population trends. This study documents a compensatory response in reproduction to changes in population size in mountain goats. The results suggest that wildlife managers can expect maximum reproductive response to harvest from introduced mountain goat populations which are still in the initial increase phase. However, even then goat populations are sensitive to overharvest. Managers must know the relationship between a goat population and the food resources available to predict responses to harvest. J. WILDL. MANAGE. 49(4):837-843 The population dynamics of mountain goats are still poorly understood (Adams and Bailey 1982). There is a consensus that goat populations are sensitive to overharvest due to late sexual maturity, generally low rates of kid production and/or survival, either-sex harvest, and high susceptibility to harvest in accessible areas (Foster 1977, Hall 1977, Hoefs et al. 1977, Kuck 1977, Macgregor 1977, Adams and Bailey 1982). There have been few long-term studies of the population responses of mountain goats to hunting, and the published studies available have yielded conflicting results. Kuck (1977) concluded that no surplus goats were produced and that harvest mortality was additive to natural mortality in the Pahsimeroi mountain goat population in Idaho. He found that production of kids declined as the population declined. Hebert and Turnbull (1977) found that goat productivity and yearling recruitment were lower on heavily hunted than on lightly hunted or unhunted portions of the East Kootenay Range of British Columbia. They thought it was questionable whether hunter harvest could be considered compensatory even in the most generous sense. Adams and Bailey (1982) concluded that the introduced mountain goat population in the Sawatch Range, Colorado, produced an annual surplus of 7% of the population which could be harvested. They presented evidence that kid production had declined as the population increased. Bailey and Johnson (1977) speculated that goat reproduction was influenced by population density because newly introduced herds had kid:100 older goat ratios averaging twice as high as ratios for well-established and native populations. Whether mountain goat reproduction is related to population density and whether goat populations will respond reproductively when reduced below carrying capacity are important questions for wildlife managers. I examined the survey, classification, and harvest data from an introduced mountain goat population in the Absaroka Mountains, south-central Montana, which has been subjected to varying levels of harvest, to analyze factors affecting reproduction and population trends. I thank S. T. Stewart, M. J. Thompson, L. H. Metzgar, G. Joslin, J. Hayden, T. J. Komberec, A. J. Foss, and J. J. Beecham for valuable comments on this manuscript, P. Farnes for the Soil Conserv. Serv. snow survey data, and L. H. Metzgar and R. C. McFarland for statistical advice. Besides myself, the surveys were conducted by J. Gaab, J. A. Ford, J. L. Egan, G. Erickson, A. J. Foss, and C. Simmons. This is a contribution from Mont. Fed. Aid to Wildl. Restoration Proj. W-130-R. STUDY POPULATION AND AREA The mountain goat population in the Absaroka Mountains was introduced in the northern portion of the range in three separate transplants totaling 23 goats; 5 goats in 1956, 10 in 1957, and 8 in 1958. These goats originated from a native herd on the Continental Divide in southwestern Montana. The mountain goats now occupy about 500 km2 within the Absaroka