Vancouver Island COSEWIC assessment and status report: chapter 6
Biology
Life cycle and reproduction
As for most alpine-dwelling marmots, Vancouver Island marmots are relatively long-lived and reproduce infrequently (Bryant 2005). They are not strictly monogamous; numerous cases of polygyny have been reported (Bryant 1998).
Females may become sexually mature at age 2, but most do not breed until they reach 3 or 4 years (mean = 3.6 years, SD = 1.2, n = 16). Mating generally occurs a month after emergence from hibernation in late April or early May. Gestation is 30-32 days (Keeley et al. 2003). Litter size at weaning varies from 1-7 (mean = 3.4, SD = 1.1, n = 58). Females can wean pups in consecutive years but most skip one or more years between litters (mean between-litter interval = 1.8 years, SD = 0.7, n = 20). Sex ratios of weaned pups do not differ from 1:1 in the wild, although they tend to be skewed towards males in captivity. The oldest known breeding female was 10 and the oldest marmot in captivity reached 14 years (Bryant 2005, Appendix 1).
Use of burrows
Vancouver Island marmots construct burrows to hibernate, bear young, hide from predators, and shelter. Burrows (including hibernacula) are commonly re-used over multiple years by the same individuals and social groups (Bryant 1998). Several burrow systems have been occupied for over 30 years. Escape burrows to avoid predators include shallow excavations under a rock or tree root. Burrows used overnight or as birthing chambers are more elaborate, often with multiple entrances. As with escape burrows, they typically occur under boulders or a tree root system. Hibernacula are presumably deep enough to reach below the frost-line.
Herbivory/predation
Martell and Milko (1986) identified plants eaten from fecal samples collected at 3 colonies. They concluded that marmots depend on oatgrass (Danthonia intermedia) and sedges (Carex spp.) in early spring, and shift to forbs (especially Lupinus latifolius and Eriophyllum lanatum) in summer and fall. Spreading phlox (Phlox diffusa) is important in early summer.
Diet at other colonies is unknown. Known food plants at low elevation clearcut sites include grasses, Anaphalis margariticea, Fragaria spp., Epilobium angustifolium, and Lupinus latifolius (Bryant 1998). Lupines (Lupinus latifolius) are eaten on ski runs at Mount Washington (J. Werner pers. com.).
Known predators of Vancouver Island marmots include cougars (Puma concolor), wolves (Canis lupus) and golden eagles (Aquilachrysaetus). Bryant and Page (2005) reported that predators accounted for at least 75% of the mortality of radio-tagged marmots from 1992-2005.
Physiology
Wild Vancouver Island marmots typically hibernate for approximately 210 days (mean immergence = 1 October, 95% CI = 28 September-3 October, n = 49; mean emergence = 28 April, 95% CI = 26-30 April, n = 43; Bryant and McAdie 2003). During torpor body temperature is close to 5º C. Spontaneous arousals occur for one or a few days every 10-14 days. Active-season body temperatures fluctuate between 34-29º C. Marmots adjust body temperature with posture (Melcher et al. 1990) and use burrows and “resting” boulders to avoid overheating.
Dispersal/migration
The metapopulation structure is pronounced compared to other mountain-dwelling marmots (e.g., Stephens et al. 2002). Dispersal events occur infrequently but radio-tagged 2 year olds of both sexes can make movements of 1-27 km within a few days (A. Bryant unpub. data).
Based on resightings of ear-tagged animals (Bryant 1998), maximum dispersal distance was 11.2 km. Records of solitary marmots in low elevation habitats suggest many possible dispersal distances greater than this. Bryant and Janz (1996) compiled 22 records of solitary marmots during 1972-1995, including 1 found on the beach at Courtenay (12 July 1974), 1 photographed on Mount Demers (25 July 1977), and 1 in a vegetable garden at Coombs (7 July 1980). Marmots show up in unusual places, including a woodshed in Youbou (25 June 1986), a horse stable in Nanaimo (25 September 1991), a new subdivision at Bell's Bay on the west coast (May 1992), and a boat dock at Lake Cowichan (18 May 1993). Some of these (e.g., Bell’s Bay, Cassidy, Duncan and Cedar) likely represent dispersal events > 25 km.
Interspecific interactions
Marmots commonly react to small raptors, deer and elk that pose no threat by whistling or by fleeing into burrows. They respond similarly to predators. Apart from that, they do not interact with other species.
Adaptability
Much has been written about the “adaptability” of M. vancouverensis to a human-modified landscape (Munro et al. 1985). Many marmots lived and reproduced successfully in man-made habitats; however, these habitats likely acted as population sinks (Bryant 1996, 1998). Populations that colonized ski-runs on Green Mountain or mine tailings at Mount Washington during the 1980s became extinct. Marmots have persisted on ski runs at Mount Washington, possibly because human activities deter predators there. Despite large amounts of potential habitat created by logging above 700 m, only a small fraction was ever colonized, and the overall distribution of M. vancouverensis has shrunk in the last several decades.
Vancouver Island marmots in captivity exhibit reproductive and behavioral traits comparable to wild counterparts (Bryant 2005, Blumstein et al. 2006). Captive-born marmots apparently adjust successfully when returned to the wild, eating grasses and flowers, gaining mass, whistling when predators approach, digging burrows and hibernating at appropriate times (Bryant 2007). Sample sizes are still too small to calculate survival rates, but some captive-born marmots have survived for up to 3 years and reproduced.
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