The American marten (Martes americana), also known as the American pine marten, is a member of the Mustelidae family native to North America. While sometimes referred to as simply the pine marten, this species is distinct from its Eurasian counterpart, Martes martes. The American marten's sable-like fur made them a thoroughly trapped species during the height of the North American fur trade. Trapping peaked in 1820, and populations were depleted until after the turn of the century. The Pacific marten (Martes caurina) was formerly thought to be conspecific, but genetic studies support it being a distinct species from M. americana. The Pacific marten has a more westerly distribution, hence its common name, ranging into the Pacific Northwest and south to Northern California. Seven regional subspecies have been recognized for M. americana. A fossil species (originating from the Late Pleistocene to Early Holocene) known as Martes nobilis is considered synonymous with M. americana.
Distribution and Habitat
Martes americana is broadly distributed in northern North America, ranging from the northern limit of the treeline in arctic Alaska and Canada south to New York. Its distribution extends from Newfoundland in the east to western Alaska and southwest to the Pacific coast of Canada. While their distribution is vast and continuous in Canada and Alaska, American marten distribution is limited to mountain ranges that provide preferred habitats in the northeastern and midwestern United States.
Martens were once thought to live only in old conifer forests, but further study shows that martens live in both old and young deciduous and conifer forests as well as mixed forests, including in Alaska and Canada, and south into northern New England, and the Adirondacks in New York. Groups of martens also live in the Midwest, in the Upper Peninsula of Michigan, Wisconsin and much of Minnesota. Trapping and destruction of forest habitat have reduced its numbers, but it is still much more abundant than the larger fisher. The Newfoundland subspecies (M. a. americana) is endemic to that province.
A broad, natural hybrid zone between the Pacific and American martens is known to exist in the Columbia Mountains, as well as Kupreanof and Kuiu Islands in Alaska. Several translocations of American marten have been made without regard to the Pacific marten, threatening the latter species. On Dall Island, American martens have been introduced and are hybridizing with the native Pacific marten population, which may put them at risk. On many islands throughout the Alexander Archipelago, American martens have been introduced and are present, with no sign of the Pacific martens; it is unknown whether the islands previously had no marten species until American martens were introduced, or whether the Pacific martens existed on those islands previously but were extirpated by the introduced American martens.
Physical Characteristics and Activity
The American marten is a long, slender-bodied weasel about the size of a mink with relatively large, rounded ears, short limbs, and a bushy tail. American marten have a roughly triangular head and sharp nose. Their long, silky fur ranges in color from pale yellowish buff to tawny brown to almost black. Their head is usually lighter than the rest of their body, while their tail and legs are darker. Total length ranges from 1.5 to 2.2 feet (0.5-0.7 m), with tail length of 5.4 to 6.4 inches (135-160 mm), Adult weight ranges from 1.1 to 3.1 pounds (0.5-1.4 kg) and varies by age and location. Other than size, sexes are similar in appearance. American marten have limited body-fat reserves, experience high mass-specific heat loss, and have limited fasting endurance.
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Compared to other carnivores, the American marten population density is low for their body size. Home ranges are indicated by scent-marking. Several authors have reported that home range boundaries appear to coincide with topographical or geographical features.
American marten activity patterns vary by region, though in general, activity is greater in summer than in winter. American marten may be active as much as 60% of the day in summer but as little as 16% of the day in winter In north-central Ontario individuals were active about 10 to 16 hours a day in all seasons except late winter when activity was reduced to about 5 hours a day. American marten may be nocturnal or diurnal. Variability in daily activity patterns has been linked to activity of major prey species, foraging efficiency, sex, reducing exposure to extreme temperatures, season, and timber harvest. In south-central Alaska, American marten were nocturnal in autumn, with strong individual variability in diel activity in late winter. Daily distance traveled may vary by age, sex, habitat quality, season, prey availability, traveling conditions, weather, and physiological condition of the individual. One marten in south-central Alaska repeatedly traveled 7 to 9 miles (11-14 km) overnight to move between two areas of home range focal activity. One individual in central Idaho moved as much as 9 miles (14 km) a day in winter, but movements were largely confined to a 1,280-acre (518 ha) area. Juvenile American marten in east-central Alaska traveled significantly farther each day than adults (1.4 miles (2.2 km) vs. 0.9 miles (1.4 km)).
The weather may impact American marten activity, resting site use, and prey availability. A snowy habitat in many parts of the range of the American marten provides thermal protection and opportunities for foraging and resting. American marten may travel extensively under the snowpack. American marten are well adapted to snow. On the Kenai Peninsula, individuals navigated through deep snow regardless of depth, with tracks rarely sinking >2 inches (5 cm) into the snowpack.
Social Behavior and Reproduction
Adult American marten are generally solitary except during the breeding season. They are polygamous, and females may have multiple periods of heat. Females enter estrus in July or August, with courtship lasting about 15 days. Embryonic implantation is delayed until late winter, with active gestation lasting approximately two months. Females give birth in late March or April to a litter ranging from 1 to 5 kits. Annual reproductive output is low according to predictions based on body size.
Females use dens to give birth and to shelter kits. Dens are classified as either natal dens, where parturition takes place, or maternal dens, where females move their kits after birth. American marten females use a variety of structures for natal and maternal denning, including the branches, cavities or broken tops of live trees, snags, stumps, logs, woody debris piles, rock piles, and red squirrel (Tamiasciurus hudsonicus) nests or middens. Females prepare a natal den by lining a cavity with grass, moss, and leaves. They frequently move kits to new maternal dens once kits are 7-13 weeks old. Most females spend more than 50% of their time attending dens in both pre-weaning and weaning periods, with less time spent at dens as kits aged. Weaning occurs at 42 days. Young emerge from dens at about 50 days but may be moved by their mother before this. In northwestern Maine, kits were active but poorly coordinated at 7 to 8 weeks, gaining coordination by 12 to 15 weeks.
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Dietary Habits
American marten are opportunistic predators, influenced by local and seasonal abundance and availability of potential prey. They require about 80 cal/day while at rest, the equivalent of about three voles (Microtus, Myodes, and Phenacomys spp.). Voles dominate diets throughout the American marten's geographic range, though larger prey-particularly snowshoe hares and American red squirrels-may be important, particularly in winter. Red-backed voles (Myodes spp.) are generally taken in proportion to their availability, while meadow voles (Microtus spp.) are taken in excess of their availability in most areas.
American marten diet may shift seasonally or annually. Generally, diet is more diverse in summer than winter, with summer diets containing more fruit, nuts, vegetation, and insects. Diet is generally more diverse with the American marten's distribution compared to Pacific marten's, though there is high diversity in the Pacific states.
American marten may be important seed dispersers; seeds generally pass through the animal intact, and seeds are likely germinable. One study from Chichagof Island, southeast Alaska, found that Alaska blueberry (Vaccinium alaskensis) and oval leaf huckleberry (V. ovalifolium) seeds had higher germination rates after passing through the gut of American marten compared to seeds that dropped from the parent plant.
Lifespan and Survival
American marten in captivity may live for 15 years. The oldest individual documented in the wild was 14.5 years old. Survival rates vary by geographic region, exposure to trapping, habitat quality, and age. In an unharvested population in northeastern Oregon, the probability of survival of American marten ≥9 months old was 0.55 for 1 year, 0.37 for 2 years, 0.22 for 3 years, and 0.15 for 4 years. The mean annual probability of survival was 0.63 for 4 years. In a harvested population in east-central Alaska, annual adult survival rates ranged from 0.51 to 0.83 over 3 years of study. Juvenile survival rates were lower, ranging from 0.26 to 0.50. In Newfoundland, annual adult survival was 0.83.
American marten are vulnerable to predation from raptors and other carnivores. The threat of predation may be an important factor shaping American marten habitat preferences, a hypothesis inferred from their avoidance of open areas and behavioral observations of the European pine marten (Martes martes). Specific predators vary by geographic region.
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