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. In winter, individuals may go into shallow torpor daily to reduce heat loss. 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 (66% active) than in late winter and early spring (43% active). 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. Activity occurred throughout the day in late winter and early spring. 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 2 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-mile (1.4 km)). Weather factors The weather may impact American marten activity, resting site use, and prey availability. Individuals may become inactive during storms or extreme cold. In interior Alaska, a decrease in above-the-snow activity occurred when ambient temperatures fell below −4F (−20C). 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. Subnivean travel routes of >33 feet (10 m) on the Upper Peninsula of