American mink

The American mink differs from members of the genus Mustela (stoats and weasels) by its larger size and stouter form, which closely approach those of martens. It shares with martens a uniformly enlarged, bushy and somewhat tapering tail, rather than a slenderly terete tail with an enlarged bushy tip, as is the case in stoats. The American mink is similar in build to the European mink, but the tail is longer (constituting 38–51% of its body length). The American mink has a long body, which allows the species to enter the burrows of prey. Its streamlined shape helps it to reduce water resistance whilst swimming. The skull is similar to that of the European mink, but is more massive, narrower, and less elongated, with more strongly developed projections and a wider, shorter cranium. The upper molars are larger and more massive than those of the European mink. The dental formula is 3.1.3.13.1.3.2. Domestic mink, which are bred in fur farms and are substandard genetically, have 19.6% smaller brains, 8.1% smaller hearts, and 28.2% smaller spleens than wild mink. The feet are broad, with webbed digits. It generally has eight nipples, with one pair of inguinal teats and three pairs of abdominal teats. The adult male's penis is 2.2 in (5.6 cm) long, and is covered by a sheath. The baculum is well-developed, being triangular in cross section and curved at the tip. Males measure 13–18 in (34–45 cm) in body length, while females measure 12–15 in (31–37.5 cm). The tail measures 6–10 inches (15.6–24.7 cm) in males and 6–8 in (14.8–21.5 cm) in females. Weights vary with sex and season, with males being heavier than females. In winter, males weigh 1–3 lb (500–1,580 g) and females 1–2 lb (400–780 g). Maximum heaviness occurs in autumn.