Mountain Goats in Olympic National Park: Biology and Management of an Introduced Species
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Mountain goats (Oreamnos americanus), introduced to the Olympic Mountains during the 1920's, are regarded now by the National Park Service as unwelcome additions to the unique biota of Olympic National Park (3,700 km2). We report results of studies of mountain goat biology and of management activities conducted in 1981-92. Thirty-five endemic forms of plants and animals are currently recognized on the Olympic Peninsula. The native mammalian fauna and the coniferous flora are impoverished compared to the nearby Cascade Mountains (12 fewer mammals, 5 fewer conifers). Goats colonized the Olympic Mountains in about 60 years. The goat population consisted of quasi-independent subpopulations that grew and declined asynchronously. The metapopulation was estimated by helicopter census to be 1,175 ± 171 (SE) goats in 1983 and 389 ± 106 in 1990; National Park Service removals contributed to the population decline. Mountain goats were removed from the Klahhane Ridge subpopulation to examine changes in demography and physical condition. Initial breeding age declined, litter size increased, and production and recruitment of kids were less variable at lowered goat densities. Changes in demography were associated with increases in live weights and fat reserves. Marked differences in reproductive performance occurred among females. Mountain goats were seasonally migratory and occupied subalpine and alpine areas above 1,520 m during summer. Goats were closely associated with rocks and cliffs at all seasons and ate a wide variety of foods, including four endemic plant taxa. Group size averaged less than three goats during summer and winter. Eighty-four percent of 125 goats tagged on Klahhane Ridge showed fidelity to summer ranges, some for 5-10 years. Interspecific competition for resources between mountain goats and the native fauna could not be demonstrated from the scant data available. Our work demonstrated that introduced mountain goats changed the vegetation of the Olympic Mountains, a finding held in common with all other studies of ungulate grazing systems. Six hundred ninety-nine plots showed that goat herbivory was distributed throughout the park above 1,520 m. Permanent vegetation plots on summer ranges showed that mountain goat herbivory changed the composition of subalpine meadows; disturbance-oriented species (e.g., Achillea millefolium) increased and selected forage species declined (e.g., Festuca idahoensis). The cover of selected forage species was negatively correlated with mountain goat density at sites with initially high levels of goat herbivory. Sixty-six photographic comparisons from Klahhane Ridge also showed that cover of disturbance-oriented species and the amount of exposed mineral soil were related to goat densities. Mountain goat summer range and the habitat of 33 rare plant taxa—including 7 peninsula endemics—overlapped considerably. Mountain goats affected and killed individual rare plants by grazing, wallowing, and trampling, but our preliminary studies could not determine trends in rare plant populations subjected to goat herbivory. Circumstantial evidence suggested that goat herbivory may have reduced densities of the rare endemic Astragalus australis var. olympicus on Mount Angeles compared to Blue Mountain. Effects of goats on Astragalus were sporadic—sometimes intense—and had unknown long-term consequences to the survival of the species. Goat management in the park during the 1980's occurred as an experimental management program (1981-87) and as operational management (1988-89). About 693 mountain goats were captured from 1977 to 1989, and personnel gained considerable experience with different capture and removal techniques. During 1981-89, 407 goats were removed from the park. The operational management program was terminated in 1989, when continued goat capture posed unacceptable risks to the capture team. Field sterilizations were attempted on 19 goats (13 females, 6 males) to evaluate this control technique. The cost and effort required to implement four strategic management options in the future (ranging from elimination to allowing the entire mountain goat population to achieve ecological carrying capacity) were explored using population models. All control or elimination options will be difficult and expensive to achieve in practice. Tactical options available for elimination or intense control of goats are limited to shooting and aerial live capture; currently available sterilization techniques could, at best, partially control the population.

Key words: Biogeography, demography, exotic species, grazing, herbivory, management, mountain goat, national park management, Olympic National Park, Olympic Peninsula, Oreamnos americanus, population estimates, rare plants.

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Last Updated: 12-Dec-2007