American ermine

American ermine
Near Beaverhill Lake, Alberta
Conservation status
Secure  (NatureServe)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Mustelidae
Genus:	Mustela
Species:	M. richardsonii
Binomial name
Mustela richardsonii Bonaparte, 1838
Subspecies
See text
Synonyms
Mustela erminea richardsonii Neogale richardsonii

The American ermine or American stoat (Mustela richardsonii) is a species of mustelid native to most of North America. The specific epithet refers to Arctic explorer and naturalist John Richardson.

Description

The American ermine has a body plan typical of weasels. It has short legs, a long body and neck, and a small triangular head with short round ears. It has a brown dorsum with a white venter (except during winter when the coat is fully white) and a short, black-tipped tail.

Taxonomy

It was long considered conspecific with the stoat (M. erminea), but a 2021 study found it to be a distinct species, forming distinct genetic clades from erminea. The finding has been accepted by the American Society of Mammalogists. The Haida ermine (M. haidarum) is thought to be a hybrid species originating from ancient hybridization between M. erminea and M. richardsonii.

Distribution

The species is found throughout most of North America aside from most of Alaska (although it is found on some islands in southeastern Alaska), eastern Yukon, most of Arctic Canada, and Greenland, where it is replaced by M. erminea. It reaches the northern extent of its range in Ellesmere Island and a portion of eastern mainland Nunavut and ranges from here to cover almost all of western North America south to northern New Mexico, and eastern North America south to northern Virginia. It is absent from most of the Southeastern United States and the Great Plains.

Diet

In North America, where the ecological niche for rat- and rabbit-sized prey is taken by the larger long-tailed weasel (Neogale frenata), the American ermine preys on mice, voles, shrews, young cottontails, chipmunks, deer mice, jumping mice, and house mice. Usually the ermine kills by biting at base of skull. Small birds, frogs, small fish, and earthworms are other types of prey for ermines.

Habitat

Ermines live and find cover from predators in hollow spaces from logs, burrows and man made structures. Ermines sometimes den within their prey's nest and use their skin and fur as a lining for their den.

Breeding

They breed in dense parts of the forest. The season for breeding is late springtime to the summer from July to August. The males mature in a year while the females only take three to four weeks to mature. The females carry a litter of four to seven babies for 255 days then gives birth.

Predators

Some of the larger wild predators of ermines are minks, martens, fishers, bobcats, coyotes, and large owls and hawks. Occasionally a domesticated cat or dog may kill an ermine. Their small agile bodies help them evade these predators, while also allow them to compete with their predators for food in more barren months.

Subspecies

About 13 subspecies are known:

Subspecies	Trinomial authority	Description	Range	Synonyms
Junean stoat M. r. alascensis.	Merriam, 1896	Similar to M. r. richardsonii, but with a broader skull and more extensive white tips on the limbs	Juneau, Alaska
Vancouver Island stoat M. r. anguinae	Hall, 1932		Vancouver Island
Western Great Lakes stoat M. r. bangsi	Hall, 1945		The region west of the Great Lakes	cicognani (Mearns, 1891) pusillus (Aughey, 1880)
Bonaparte's stoat M. r. cigognanii	Bonaparte, 1838	A small subspecies with a dark brown summer coat; its skull is more lightly built than that of richardsonii.	The region north and east of the Great Lakes	pusilla (DeKay, 1842) vulgaris (Griffith, 1827)
M. r. fallenda	Hall, 1945
M. r. gulosa	Hall, 1945
M. r. initis	Hall, 1945
M. r. invicta	Hall, 1945
Southwestern stoat or New Mexico ermine M. r. muricus	Bangs, 1899	The smallest subspecies of richardsonii.	The southwestern extremity of the species' American range (Nevada, Utah, Colorado and other states)	leptus (Merriam, 1903)
Olympic stoat M. r. olympica	Hall, 1945		The Olympic Peninsula, Washington
Richardson's stoat M. r. richardsonii	Bonaparte, 1838	Similar to M. r. cigognanii, but larger, with a dull chocolate brown summer coat	Newfoundland, Labrador and nearly all of Canada (save for the ranges of other American stoat subspecies)	imperii (Barrett-Hamilton, 1904) microtis (J. A. Allen, 1903) mortigena (Bangs, 1913)
Baffin Island stoat M. r. semplei	Sutton and Hamilton, 1932		Baffin Island and the adjacent parts of the mainland	labiata (Degerbøl, 1935)
M. r. stratori	Merriam, 1896

Relationships with humans

The fur of ermine was valued by the Tlingit and other indigenous peoples of the Pacific Northwest Coast. They could be attached to traditional regalia and cedar bark hats as status symbols or made into shirts.

Gallery

• 
  American ermine surplus killing a family of chipmunks, as illustrated by Ernest Thompson Seton
• 
  Skulls of a long-tailed weasel (top), an American ermine (bottom left), and least weasel (bottom right), as illustrated in Merriam's Synopsis of the Weasels of North America
• 
  Winter coat

Bibliography

• Merriam, Clinton Hart (1896). Synopsis of the weasels of North America. Washington, D.C.: Govt. Print. Off.
• Verts, B. J.; Carraway, Leslie N. (1998). Land Mammals of Oregon. University of California Press. ISBN 0-520-21199-5.