Open-File Report 2011-1313
This report has been superseded by Jenkins, K.J., Happe, P.J., Beirne, K.F., Hoffman, R.A., Griffin, P.C., Baccus, W.T., and Fieberg, John, 2012, Recent population trends of mountain goats in the Olympic Mountains, Washington: Northwest Science, v. 86, pp. 264-275.
We conducted an aerial helicopter survey between July 18 and July 25, 2011, to estimate abundance and trends of introduced mountain goats (Oreamnos americanus) in the Olympic Mountains. The survey was the first since we developed a sightability correction model in 2008, which provided the means to estimate the number of mountain goats present in the surveyed areas and not seen during the aerial surveys, and to adjust for undercounting biases. Additionally, the count was the first since recent telemetry studies revealed that the previously defined survey zone, which was delineated at lower elevations by the 1,520-meter elevation contour, did not encompass all lands used by mountain goats during summer. We redefined the lower elevation boundary of survey units before conducting the 2011 surveys in an effort to more accurately estimate the entire mountain goat population. We surveyed 39 survey units, comprising 39 percent of the 59,615-hectare survey area. We estimated a mountain goat population of 344+44 (standard error, SE) in the expanded survey area. Based on this level of estimation uncertainty, the 95-percent confidence interval ranged from 258 to 430 mountain goats at the time of the survey.
To permit comparisons of mountain goat populations between the 2004 and 2011 surveys, we recomputed population estimates derived from the 2004 survey using the newly developed bias correction methods, and we computed the 2004 and 2011 surveys based on comparable survey zone definitions (for example, using the boundaries of the 2004 survey). The recomputed estimates of mountain goat populations were 217+19 (SE) in 2004 and 303+41(SE) in 2011. The difference between the current 2011 population estimate (344+44[SE]) and the recomputed 2011 estimate (303+41[SE]) reflects the number of mountain goats counted in the expanded lower elevation portions of the survey zone added in 2011. We conclude that the population of mountain goats has increased in the Olympic Mountains at an average rate of 4.9+2.2(SE) percent annually since 2004. We caution that the estimated rate of population growth may be conservative if severe spring weather deterred some mountain goats from reaching the high-elevation survey areas during the 2011 surveys. If the estimated average rate of population growth were to remain constant in the future, then the population would double in approximately 14–15 years.
First posted February 9, 2011
For additional information contact:
Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.
Jenkins, K., Happe, P., Griffin, P., Beirne, K., Hoffman, R., and Baccus, B., 2011, Mountain goat abundance and population trends in the Olympic Mountains, Washington, 2011: U.S. Geological Survey Open-File Report 2011-1313, 22 p.
Study Area and Methods
Appendix 1. Incidental Observations of Other Wildlife Species by Survey Unit, Olympic Mountains, Washington, 2011
Appendix 2. Trends in Other Wildlife Species Seen during Goat Surveys in the Olympic Mountains, Washington, 1983–2011
Appendix 3. Survey Flight Characteristics during Aerial Mountain Goat Surveys, Olympic Mountains, Washington, 2011
Appendix 4. Survey Characteristics and Environmental Conditions Measured at the Beginning of Each Unit Surveyed in the Olympic Mountains, Washington, 2011
Appendix 5. Raw Counts of Mountain Goats by Survey Unit, Olympic Mountains, Washington, 2011