The Olympic marmot (Marmota olympus) is a rodent in the squirrel family, Sciuridae. It occurs only in the U.S. state of Washington, at the middle elevations of the Olympic Peninsula. The closest relatives of this species are the hoary marmot and the Vancouver Island marmot. In 2009, it was declared the official endemic mammal of Washington state.
This marmot is about the size of a domestic cat, typically weighing about in summer. The species shows the greatest sexual dimorphism found in marmots, with adult males weighing on average 23% more than females. It can be identified by a wide head, small eyes and ears, stubby legs, and a long, bushy tail. Its sharp, rounded claws aid in digging burrows. The coat color changes with the season and with age, but an adult marmot's coat is brown all over with small white areas for most of the year.
The species has a diet consisting mainly of a variety of meadow flora, including dry grasses, which it also uses as bedding in burrows. It is preyed on by various terrestrial mammals and avian raptors, but its main predator today is the coyote. However, the complex system of communication through whistling means most marmots remain safe for their entire life. The Olympic marmot is rated a species of the least concern on the IUCN Red List. It is protected by law in the Olympic National Park, which contains most of its habitat.
The burrows of this marmot are made in colonies, which are found in various mountain locations and differ in size. A colony may contain as few as one marmot family or multiple families with up to 40 marmots. Olympic marmots are very sociable animals which often engage in play fighting and vocalize four different whistles to communicate. During hibernation, which begins in September, they are in a deep sleep and do not eat, causing them to lose half their body mass. Adults emerge in May and their young in June. Female marmots reach sexual maturity at three years of age and produce litters of 1–6 young every other mating season.
Taxonomy
American zoologist and ethnographer Clinton Hart Merriam first formally described the Olympic marmot in 1898, as Arctomys olympus, from a specimen he and Vernon Orlando Bailey collected on the Sol Duc River. The genus, Arctomys, is from the Greek for "bear-mouse". The species name, olympus (Olympic in Greek), was given because this species is native to the Olympic Peninsula. The species now is classified with all other marmots in the genus Marmota. Zoologist R. L. Rausch classified the Olympic marmot as the subspecies olympus of Marmota marmota (he included all North American marmots in this species, which now only includes the Eurasian Alpine marmot) in 1953, but it has usually been treated as a distinct species, a classification supported by taxonomic reviews starting with that of zoologist Robert S. Hoffmann and colleagues in 1979.
Within Marmota, the Olympic marmot is grouped with species such as the hoary marmot (M. caligata) in the subgenus Petromarmota. Among this grouping, mitochondrial DNA analyses suggest that the Olympic marmot could be the sister species to all other species in the group. The Olympic marmot is thought to have originated during the last glacial period as an isolated relict population of the hoary marmot in the Pleistocene ice-free refugia. As of October 2011, molecular data indicate that the most recent common ancestor of the Olympic marmot and its closest relatives lived 2.6 million years ago.
The Olympic marmot deviates from the typical Petromarmota marmots in the shape and large size of its mandible (jawbone), in differences of the dorsal (back) region, and having 40 chromosomes instead of 42, all of which are characteristics that resemble the subgenus Marmota. Some of the differences of the Olympic marmot's jawbone from the typical Petromarmota are also evident in the Vancouver Island marmot (M. vancouverensis), which evolved separately, but also occurs in a restricted range with a small population.
Description
The Olympic marmot's head is wide with small eyes and ears; the body is stocky with stubby legs and sharp, rounded claws that facilitate digging; the tail is bushy and ranges from long. The Olympic marmot is about the size of a domestic cat; adults typically weigh from and are from in length, with the average being . This species may have the most pronounced sexual dimorphism found in marmots, with adult males weighing on average , post emergence in spring and at peak weights in autumn, respectively, and adult females weighing at the same times. The Olympic marmot is the largest of the six marmot species found in North America, averaging slight heavier in mean body mass than hoary marmot and Vancouver marmot. Mean linear dimensions suggest the Olympic species is about 7% larger on average than these other two large North American species. The species rivals some lesser-studied Asian species as the largest marmots and largest members of the squirrel family, with similar body masses attained by some species such as the Tarbagan marmot and the Himalayan marmot.
The coat is double-layered, consisting of soft, thick underfur, for warmth, and coarser outer hairs. Infant marmots' fur is dark gray in color; this changes in the yearling period to grayish brown with lighter patches. The adult coat is brown on the body with some smaller white or pale brown patches for most of the year, becoming darker overall as the year progresses. The first molt of the year occurs in June, commencing with two black patches of fur forming on the back of the shoulders. This black coloration then spreads to the rest of the body, and by the fall the coat is almost black. A second molt is thought to occur during hibernation, and upon emergence from hibernation in the spring Olympic marmots may be tan or yellowish. The Olympic marmot's muzzle is almost always white, with a white band in front of the eyes.
This species can be readily distinguished from the hoary marmot, with which it shares almost every other physical trait, by the lack of contrasting black feet and a black spot on the head. The Vancouver Island marmot has a similar coat color—chocolate brown with white patches.
Distribution and habitat
Olympic marmots are native to the Olympic Mountains in the Olympic Peninsula of Washington state. About 90% of Olympic marmots' total habitat is located in Olympic National Park, where they are often sighted, especially on Hurricane Hill. Marmots are in decline in some areas of the park due to encroachment by trees into meadows as well as predation by coyotes, and they are seldom seen in the wetter southwestern part.
Within the park, Olympic marmots inhabit lush sub-alpine and alpine meadows, fields, and montane scree slopes. They live in colonies spread out in various locations in the mountains and containing the burrows of varied numbers of marmot families. Some meadows can contain as few as one marmot family, while some can have multiple families, amounting to as many as 40 marmots. There is a higher risk of inbreeding and death from random events in meadows with fewer marmots, making migration essential to the survival of the species. Burrows can be found at elevations ranging from to ; they are most often found in the range of to . Burrows are more frequently located on south-facing slopes, which generally receive more precipitation, per year (mostly snow), and thus have more available flora. The home range of a family of marmots usually covers from half an acre to five acres (0.2–2 hectares). The Olympic marmot is well-adapted to its generally cold natural habitat, where there is snowfall almost every month of the year on the mountain slopes and barren grasslands.
Ecology Feeding
Olympic marmots eat meadow flora such as avalanche and glacier lilies, heather blossoms, subalpine lupine, mountain buckwheat, harebells, sedges, and mosses. They prefer green, tender, flowering plants over other sources of food, but roots are a large part of their diets in the early spring when other plants have not yet appeared. During May and June, they may resort to gnawing on trees for food. They also occasionally eat fruits and insects. Their water requirements are met by the juice in the vegetation they eat and dew on the plants' surfaces.
When snowfall covers vegetation, marmots have a more omnivorous diet, consuming carrion encountered while digging for roots and possibly killing late hibernating chipmunks (Neotamias townsendii). At this time, they also obtain water from melted snow. Hibernating Olympic marmots do not keep food in their burrows; instead, they put on fat before hibernating and can double their body weight to survive eight months without eating.
Predation
The Olympic marmot's predators are mostly terrestrial mammals such as coyotes, cougars, and bobcats; however, it is also preyed on by avian raptors such as golden eagles. Evidently, black bears rarely prey on marmots—bears' presence close to colonies generally does not elicit alarm calls, unless the bear advances to within of the colony. The coyote is the Olympic marmot's primary predator, and studies show that marmots make up approximately 20% of coyotes' diet during the summer months.
In common with all other marmots, Olympic marmots use an alarm call known as a trill to alert other marmots to predators. Continuing alarm calls indicate that a predator is close, and cause marmots to display increased vigilance; a single alarm call results in the marmots curiously looking around for the predator. Sightings of land predators, especially coyotes, receive more alarm calls than aerial predators. Fishers are viewed as predators by Olympic marmots, eliciting alarm calls even when just passing by a colony. Trill calls have also been observed being used to trick and frustrate predators. When a marmot becomes nervous or bothered by a predator, it may retract its top lip to show its upper incisors.
David P. Barash reported that when hunting Olympic marmots, a coyote or cougar approach a marmot to within about , advance to a fir tree close to its prey, and then chase the marmot from uphill.
As humans in the Olympic National Park do not hunt the marmot, but simply observe them, they do not pose a threat to them. When researchers intrude on colonies to observe behavior, the families living in burrows there initially make ascending calls, showing surprise, but later adjust to the presence of humans, allowing studies to proceed.
Parasites of the Olympic marmot include Diandrya composita and fleas of the genus Oropsylla.
Behavior Colonies
Olympic marmots are gregarious burrowing animals, living in colonies typically containing multiple burrows. Activity varies with the weather, time of day, and time of year. Due to rainfall and fog cover during June, July, and August, marmots spend most of the day inside their burrows during these months, and emerging to forage for food mostly in the morning and evening. At other times of year, Olympic marmots can sometimes be found lying on rocks where they sun themselves for warmth, grooming each other, playing, chirping, and feeding together. Burrows are used for hibernation, protection from bad weather and predators, and to raise newborn pups.
A typical colony consists of a male, two to three females, and their young, totalling a dozen or more animals. Young marmots stay with their family for at least two years, so a burrow is often home to a newly born litter and a litter of two-year-olds. Marmots seldom move to other colonies with the exception of sub-adults of two to three years old, which may leave the home colony to start a new family elsewhere; females move only a few hundred meters, while males often move several kilometers away from their birth burrow.