American marten

Appearance

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 the tail and legs are darker. American marten usually have a characteristic throat and chest bib ranging in color from pale straw to vivid orange. Sexual dimorphism is pronounced, with males averaging about 15% larger than females in length and as much as 65% larger in body weight. Body length ranges from 1.5 to 2.2 feet . Adult weight ranges from 1.1 to 3.1 pounds 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 a limited fasting endurance. In winter, individuals may go into shallow torpor daily to reduce heat loss.

Distribution

The American marten is broadly distributed in northern North America. From north to south its range extends from the northern limit of treeline in arctic Alaska and Canada to northern New Mexico. From east to west its distribution extends from Newfoundland and south west to Napa County, California. In Canada and Alaska, American marten distribution is vast and continuous. In the western United States, American marten distribution is limited to mountain ranges that provide preferred habitat. Over time, the distribution of American marten has contracted and expanded regionally, with local extirpations and successful recolonizations occurring in the Great Lakes region and some parts of the Northeast. The American marten has been reintroduced in several areas where extinction occurred.


The marten lives in mature coniferous or mixed forests in Alaska and Canada, the Pacific Northwest of the United States and south into Northern New England and through the Rocky Mountains and Sierra Nevada. Small groups of martens live in the Midwest in Minnesota and Wisconsin. Trapping and destruction of forest habitat have reduced its numbers, but it is still much more abundant than the larger fisher. The Newfoundland subspecies of this animal is considered to be threatened.

Behavior

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. In south-central Alaska, American marten were more active in autumn than in late winter and early spring . In northeastern California, more time was spent traveling and hunting in summer than in winter, suggesting that reduced winter activity may be related to thermal and food stress or may be the result of larger prey consumption and consequent decrease in time spent foraging.

American marten may be nocturnal or diurnal. Variability in daily activity patterns has been linked to activity of major prey species, foraging efficiency, gender, reducing exposure to extreme temperatures, season, and timber harvest. In northeastern California, activity in the snow-free season was diurnal, while winter activity was largely nocturnal. In south-central Alaska, American marten were nocturnal in autumn, with strong individual variability in diel activity in late winter. Activity occurred throughout the day in late winter and early spring.

Daily distance traveled may vary by age, gender, habitat quality, season, prey availability, traveling conditions, weather, and physiological condition of the individual. Year-round daily movements in Grand Teton National Park ranged from 0 to 2.83 miles , averaging 0.6 mile . One marten in south-central Alaska repeatedly traveled 7 to 9 miles overnight to move between 2 areas of home range focal activity. One individual in central Idaho moved as much as 9 miles a day in winter, but movements were largely confined to a 1,280-acre area. Juvenile American marten in east-central Alaska traveled significantly farther each day than adults vs. 0.9 mile ).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, witch's brooms, rock piles, and red squirrel 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 preweaning and weaning periods, with less time spent at dens as kits aged. Paternal care has not been documented.

Habitat

The American marten is broadly distributed in northern North America. From north to south its range extends from the northern limit of treeline in arctic Alaska and Canada to northern New Mexico. From east to west its distribution extends from Newfoundland and south west to Napa County, California. In Canada and Alaska, American marten distribution is vast and continuous. In the western United States, American marten distribution is limited to mountain ranges that provide preferred habitat. Over time, the distribution of American marten has contracted and expanded regionally, with local extirpations and successful recolonizations occurring in the Great Lakes region and some parts of the Northeast. The American marten has been reintroduced in several areas where extinction occurred.


The marten lives in mature coniferous or mixed forests in Alaska and Canada, the Pacific Northwest of the United States and south into Northern New England and through the Rocky Mountains and Sierra Nevada. Small groups of martens live in the Midwest in Minnesota and Wisconsin. Trapping and destruction of forest habitat have reduced its numbers, but it is still much more abundant than the larger fisher. The Newfoundland subspecies of this animal is considered to be threatened.

Reproduction

American marten reach sexual maturity by 1 year of age, but effective breeding may not occur before 2 years of age. In captivity, 15-year-old females bred successfully. In the wild, 12-year-old females were reproductive.

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 a month. 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. Fecundity varies by age and year and may be related to food abundance.

Food

American marten are opportunistic predators, influenced by local and seasonal abundance and availability of potential prey. They require about 80 kcal/day while at rest, the equivalent of about 3 voles . Voles dominate diets throughout the American marten's geographic range, though larger prey—particularly snowshoe hares—may be important, particularly in winter. Red-backed voles are generally taken in proportion to their availability, while meadow voles are taken in excess of their availability in most areas. Deer mice and shrews are generally eaten less than expected, but may be important food items in areas lacking alternative prey species. Birds were the most important prey item in terms of frequency and volume on the Queen Charlotte Islands, British Columbia. Fish may be important in coastal areas.

American marten diet may shift seasonally or annually. In general, diet is more diverse in summer than winter, with summer diets containing more fruit, other vegetation, and insects. Diet is generally more diverse in the eastern and southern parts of American marten's distribution compared to the western part, though there is high diversity in the Pacific states. American marten exhibit the least diet diversity in the subarctic, though diversity may also be low in areas where the diet is dominated by large prey species .

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 and ovalleaf huckleberry seeds had higher germination rates after passing through the gut of American marten compared to seeds that dropped from the parent plant. Analyses of American marten movement and seed passage rates suggested that American marten could disperse seeds long distances: 54% of the distances analyzed were >0.3 mile .The fur of the American marten is shiny and luxuriant, resembling that of the closely related sable. At the turn of the twentieth century, the American marten population was depleted due to the fur trade. The Hudson's Bay Company traded in pelts from this species among others. Numerous protection measures and reintroduction efforts have allowed the population to increase, but deforestation is still a problem for the marten in much of its habitat. American marten are trapped for their fur in all but a few states and provinces where they occur. The highest annual trapping rate in North America was in 1820 .

Trapping is a major source of American marten mortality in some populations and may account for up to 90% of all deaths in some areas. Overharvesting has contributed to local extirpations. Trapping may impact population density, sex ratios and age structure. Juveniles are more vulnerable to trapping than adults, and males are more vulnerable than females. American marten are particularly vulnerable to trapping mortality in industrial forests.

Predators

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 from behavioral observations of the European pine marten . Specific predators vary by geographic region. In Newfoundland, red foxes were the most frequent predator, though coyote and other American marten were also responsible for some deaths. In deciduous forests in northeastern British Columbia, most predation was attributed to raptors. Of 18 American marten killed by predators in northeastern Oregon, 8 were killed by bobcats , 4 by raptors, 4 by other American marten, and 2 by coyotes. Throughout the distribution of American marten, other predators include the great horned owl , bald eagle , golden eagle , Canada lynx , mountain lion , fisher , wolverine , grizzly bear , American black bear , and gray wolf . In northeastern Oregon, most predation occurred between May and August, and no predation occurred between December and February.