Alaska marmot

The Alaska marmot's ancestry traces to the Pleistocene epoch.[8] There are no known fossils of Marmota broweri.[10] However, a fossil reportedly belonging to M. flavescens that is dated to the Late Pleistocene, recovered from the Trail Creek Caves on the Seward Peninsula[11] has been hypothesized as being an incorrect identification of an M. broweri fossil.[10]

The evolutionary lineages of the 14 marmot species distributed across the Holarctic are relatively ambiguous.[12] Cytochrome b sequences indicated that M. broweri is most likely related to M. caudata, M. menzbieri, M. marmota, and M. monax.[12] In support to the cytochrome b results, experimentation involving mitochondrial DNA has suggested that M. broweri is most likely related to M. caudata and M. menzbieri. However, morphological data have linked M. broweri to M. camtschatica.[3] In addition, somatic chromosome analysis, ecological data, and behavioral data have shown that there is a link between M. broweri and M. caligata.[8]

In terms of global distribution, the Alaska marmot is Nearctic.[10] Alaska marmots inhabit the mountains that lie north of the Yukon and Porcupine rivers in central and northern Alaska—including the Brooks Range, Ray Mountains, and Kokrines Hills.[13][10] However, there have been reports of Alaska marmots in the Richardson Mountains in the northern Yukon Territory but these sightings have not yet been confirmed.[10][14] Their overall distribution is still poorly understood.[9] The International Union for Conservation of Nature (IUCN) does not consider their population "severely fragmented," but the Alaska Department of Fish and Game has described it as "patchy."[1][9]

Alaska marmots are found scattered throughout Alaska as small colonies, each consisting of several families.[15] Their locations have been documented in the Brooks Range from Lake Peters to Cape Lisburne and Cape Sabine.[16] There have been sightings of the species near rivers in the Northern Baird mountains, in the Mulik Hills,[17] near Copter Peak in the De Long Mountains,[18] and south of the Brooks Range in the Spooky Valley and in the Kokrines Hills.[10]

The Alaska marmots are found in grassland, inland cliffs, and mountain peaks. They are located at elevations of about 1,000 metres (3,300 ft) to 1,200 metres (3,900 ft).[1] They are often found in boulder fields, rock slides and outcrops, terminal moraines, and Talus slopes[19] in Alpine tundra with herbaceous forage.[10] The species inhabits slopes surrounding lakes, and are found less commonly away from lakes.[20] Alaska marmots inhabit permanent winter dens that are used for as long as twenty years.[3] The entrances are plugged with vegetation, dirt, and feces. These dens are usually located near a ledge which functions as an observation post. A colony consists of several individual family burrows built in close proximity to one another. Their fur coloration helps them blend in amongst rocks.[19]

The retina of the eye of Alaska marmots is entirely lacking of rods, making their night vision quite poor.[3] Their eyes also lack a fovea, making their visual acuity much worse than other rodents.[3] The location of their eyes makes their field of vision very wide, sideways and upward.[3] Like other rodents, Alaska marmots have incisors that do not stop growing.[9] There is a single pair of incisors in each jaw.[3]

Compared to the very similar hoary marmot, also found in Alaska, M. broweri are much softer. They also lack the characteristic white facial patch of hoary marmots. The groundhog, another Alaskan marmot, can be told apart by its more reddish coloring, as compared to the grayer Alaskan and hoary marmots.[19]

The Alaska marmot's main nutrition source is vegetation that grows on mountain sides, which includes grasses, flowers, fruits, grains, legumes, lichen, and occasionally insects.[2][3][19] M. bromeri must eat large amounts due to the low nutritional value and the need to prepare for hibernation.[2] Alaska marmots are typically known as omnivores but they have also been described as insectivorous, folivorous, frugivorous, and granivorous.[3]

The Alaska marmot is preyed on by wolverines, gray wolves, grizzly bears, coyotes, and foxes.[19] Eagles, particularly the golden eagle, are a major predator of younger marmots.[21]

A sentry marmot will alert the colony via a two-toned, high-pitched warning call if there is a predator in the area.[19] The older marmots will defend and keep a lookout for predators while the young play. Dens dug solely in dirt provide limited protection, but a den built under rocks and boulders can prevent the risk from large animals, such as grizzly bears, who dig marmots out of their dirt-dug dens.[21]

Marmots enrich soil with uneaten food, nesting material, and their feces, and help to aerate the soil with their digging. They also serve as a food source for a variety of predators.[19]

Alaska marmots are very social, living in colonies of up to 50 while all sharing a common burrow system.[3] Marmots typically have their own personal den, while the young live with their mother and the father lives in a nearby den. Especially in large colonies, the Alaska marmots utilize sentry duty rolls that are periodically rotated.[21]

M. broweri will mark their territory by secreting a substance from face-glands and rubbing the sides of their face on rocks around their den and various trails.[8] Alaska marmots also enjoy sunbathing and spending a large amount of time in personal grooming.[3]

M. broweri is one of the longer hibernating marmots, being documented to do so up to eight months annually.[3] Alaska marmots accumulate a thick fat layer by late summer to sustain them throughout the winter hibernation.[19] Alaska marmots are active until snow begins to fall, when they will go to their hibernacula from around September until June.[2] Alaska marmots have special winter dens with a single entrance that is plugged with a mixture of dirt, vegetation, and feces during the winter hibernation period.[19] These winter dens are built on exposed ridges that thaw earlier than other areas, and the entire colony stays within the den from September until the plug melts in early May.[19] They then settle in their dens in family units to communally hibernate for the winter.[22]

Communal hibernation may be an adapted strategy to reduce metabolic cost while trying to keep their body temperatures above freezing.[22] During hibernation many of their body functions decrease such as body temperature (averages between 4.5 °C (40.1 °F) and 7.5 °C (45.5 °F)), heart rates, and respiratory rates.[21][22] Alaska marmot hibernation is not continuous because they will awaken every three or four weeks in order to urinate and defecate.[3][22] Inside the hibernaculum den, the Alaska marmot has shown long-term hibernation adaptions by their ability to tolerate high CO₂ levels and low O₂ levels.[23] As an adaption to the Arctic environment and permanently frozen ground, Alaska marmots breed prior to emerging from the winter den.[19] The Alaska marmots will generally emerge from the den during the first two weeks of May.

Male Alaska marmots are polygynous, mating with the monogamous females living on their territory. They are seasonal iteroparous and viviparous breeders that mate once in the early spring and give birth about six weeks later with litter sizes ranging from three to eight and an average litter size of four to five. The male and female Alaska marmots are involved in both raising and protecting the pups in their natal burrow. In both sexes sexual reproductive behaviors are stimulated by odors released from anal scent glands. Before birthing, the female will first close her den off and then she will give birth alone. The gestation period is about five or six weeks. Newly born Alaskan marmots are altricial;[21] hairless, toothless, blind[19] and are quite vulnerable to predators. After about six weeks young marmots have thick, soft fur and they begin to temporarily leave the den. They will go through three coats in their first year until their final one, which resembles adult Alaska marmots.[21] They will hibernate and live with their parents at least one year, they will be fully-grown after two years and reach sexual maturity from two to three years.[19][21] Marmots life span are not known but it is believed to be about thirteen to fifteen years.[21]

Although dangers of direct human disturbance are minimal, climate dangers pose a significant threat. The Alaska marmot is arguably the most sensitive of the 14 marmot species to anthropogenic disturbances, including climate change.[3]

M. broweri has been reported to have been successfully reared in captivity and reintroduced into the wild, but there have been cases where captive rearing led to high rates of mortality.[3]