Otter
Where found: They are active all of the year and are found on many streams and lakes throughout the park. Best seen near the outlet of Lewis Lake and near the boat docks at Lake and West Thumb. Active at all hours.
WESTERN MINK
Mustela vison energumenos
The mink is a large weasel of slightly heavier build and semi-aquatic in habit. Found widely distributed in forests or on plains but always along watercourses where it establishes its den. This may be a burrow in the bank, under logs or rocks and similar places.
They are strong and graceful swimmers and are fully capable of catching trout and other fish which form a part of their diet, as well as frogs and crayfish. They also hunt on shore for muskrats, mice, rabbits, snakes, birds and similar forms of small animal life. The mink is sometimes of bloodthirsty temperament, killing for the pleasure, but is not ordinarily considered quite as much inclined this way as the smaller weasels.
The odor of the musk carried by the mink as well as the other weasels is strong and very offensive. This is released in moments of excitement.
The mink has but one litter of young a year, numbering five or six in the average litter, which are born in April or May.
General description: A slender weasel-like animal nearly as large as a house cat. Ears small, neck long, tail moderately bushy. The fur is soft and dense, protected by long guard hairs, rich, glossy dark sooty brown in color with a white area under the chin. Total length 24 inches, tail 8 inches; weight up to 2 pounds, the females somewhat smaller.
Where found: Along some of the streams and ponds of the park but not very common and seldom seen.