Distribution and abundance of hoary marmots in North Cascades National Park Complex, Washington, 2007-2008

Christophersen, Roger

A 2-year systematic baseline survey of hoary marmot (Marmota caligata) distribution and abundance was conducted in North Cascades National Park Complex (NOCA) from late June to early September 2007 and 2008. Surveys sites were located in meadow habitat above 1,219 m (4,000 ft) and accessible by trail. Thirty-one sites were randomly selected from the sampling universe and surveyed using a point count sampling system spaced every 400 m along trail transects. The number of point count stations ranged from 2 to 9 (mean=4) points per survey site. Surveyors detected 242 marmots at 19 of 31 (61%) sites with abundance ranging from 0-25 individuals per site. Marmots occupied areas ranging in elevation from 1,158–2,115 m largely on south-facing slopes (54.5%). Of the 31 sites surveyed, 123 individual point count stations were established and sampled, of which 58 (47%) yielded marmot detections. Generally, all marmots detected at each point count station were collectively called a colony. However, on three occasions surveyors distinguished two colonies from a single point count station. Hence, 61 separate colonies were identified consisting of a minimum of 242 marmots. Age classifications consisted of 145 (59%) adults, 33 (14%) yearlings, 31 (13%) juveniles, and 33 (14%) animals of unknown age. Young of the year were confirmed at 13 of 31 (42%) survey sites and at 20 of 61 (33%) colonies. In 2007, all survey sites (21) were visited on one occasion only. In 2008, eight new sites were surveyed, four of which were surveyed twice to examine intra-year variability in occupancy and abundance. In addition, surveyors repeated visits to four sites reported as unoccupied in 2007 and visited four sites that were surveyed once in 2007 and again surveyed twice in 2008 to examine intra and inter-year variability in occupancy and count numbers. Eleven of 12 (92%) repeat visits showed the same results, whereas occupancy was confirmed in each of the two surveys, while one site resulted in occupancy only on the second visit. However, there were slight increases in total number of marmots counted with increasing date at 50% of sites. One of the four sites not occupied in 2007 was found to be occupied during 2008 surveys, establishing a newly discovered colony. Since marmots exist in a metapopulation dynamic, it is not certain whether this site was unoccupied in 2007 and subsequently recolonized in 2008, or if the site was actually occupied in 2007, but presence went undetected. Statistical modeling and information theoretic techniques were used to examine variables affecting marmot abundance counts. Area of each survey site and site location relative to the Cascade Mountain and Picket Range crests were significant in the top model. Marmot abundance was positively correlated with survey site area and negatively correlated with sites located west of both crests. Abundance was positively correlated with an interaction between elevation and west-side sites, suggesting that sites west of the crest supported more marmots at higher elevations. Counts may underestimate actual marmot abundance, since in all likelihood not all animals were visible during surveys and some sites were surveyed prior to expected dates of juvenile emergence. However, survey efforts were successful in describing general characteristics of marmot habitat, identifying presence and determining minimum counts of abundance and density at survey sites. This has offered insight regarding current distribution and abundance of marmots in NOCA. Recommendations are included for future monitoring using presence-absence methodology.

Distribution and abundance of hoary marmots in North Cascades National Park Complex, Washington, 2007-2008

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