Montana mammals

American Ermine in Montana

Mustela erminea

Native to Montana

Not listed as nonindigenous in Montana by USGS NAS; treated as native to its mapped Montana range.

IUCN Red List status

  1. LC
  2. NT
  3. VU
  4. EN
  5. CR
  6. EW
  7. EX

LC – Least Concern

Widespread and abundant; not at risk.

Mustela Erminea headMustela erminea hibernicaMustela erminea uprightAmerican ermine standing alert on a wooden beamAmerican ermine peering from a mossy den entranceAmerican ermine in white winter coat crossing an alpine talus slope
Photo: Keven Law from Los Angeles, USA · CC BY-SA 2.0Mustela Erminea headPhoto: Alastair Rae from London, United Kingdom · CC BY-SA 2.0Mustela erminea hibernicaPhoto: Steve Hillebrand, USFWS · Public domainMustela erminea uprightPhoto: Robbie Hannawacker · CC0American ermine standing alert on a wooden beamPhoto: miaow7477 · CC0American ermine peering from a mossy den entrancePhoto: Игорь Загребин · CC0American ermine in white winter coat crossing an alpine talus slope

American Ermine in Montana, by the numbers

Occasional in Montana 74th most recorded of 122 mammals logged in Montana

80 occurrence records

Records from 2000–2026.

80 total records count every Montana occurrence from GBIF and iNaturalist; the monthly chart covers the 78 records with a full observation date.

When to look for the American Ermine in Montana

Most sightings fall in July to October.

78 Montana occurrence records (iNaturalist and GBIF) by month of year, 2000–2026. Shows when the species is recorded, not a guarantee of presence.

Monthly Montana records (table)
MonthRecords
January5
February7
March3
April1
May0
June6
July10
August10
September12
October8
November7
December9

Monthly american ermine occurrence records (iNaturalist and GBIF) in Montana, 2000–2026.

Seasonality

Year-round in Montana, with recorded sightings peaking in July–October, with a smaller rise in December.

Occurrence map

Where American Ermine has been recorded in Montana

80 records mapped · zoom and drag to explore

80 Montana records mapped

Notable places to look

Park, forest, or monumentiNaturalist records
Glacier National Park 8
Lolo National Forest 6
Flathead National Forest 2
Kootenai National Forest 2
Council Grove State Park 1
Lubrecht State Experimental Forest 1
Flathead Lake/Wild Horse Island State Park 1

Protected places with the most american ermine sightings, from the USGS Protected Areas Database plus named mountain ranges, good spots to look, not a full breakdown, so they don't sum to the total.

Where it's recorded in Montana

CountyRecords
Missoula County 18
Ravalli County 12
Glacier County 8
Lake County 8
Lincoln County 8
Flathead County 7
Mineral County 5
Beaverhead County 3
Gallatin County 2
Sanders County 2
Meagher County 2
Park County 1
4 other counties 4

The complete county distribution, spread across 16 Montana counties. Every occurrence record falls in one county, so these sum to the total. Counties from GBIF and US Census boundaries.

American ermine records in Montana cluster around Red Rock Lakes, Flathead Lake, and the Missouri River corridor, spanning wetland, lake, and river habitat where this small weasel hunts voles and other small rodents along brushy edges. All 80 records come from GBIF rather than photographs.

Reports climb from August through December, a long, uneven build that likely tracks survey and trapping timing more than a single seasonal peak. NatureServe treats the species as native to its mapped Montana range.

Occurrence data from iNaturalist.

Mustela Erminea head
Full species profile American Ermine Mustela erminea Size 17–33 cm6.7–13 in Weight 70–260 g2.5–9.2 oz Lifespan Up to 12.5 yr View the full profile

More mammals in Montana in the atlas

Data & sources

The data and visualizations on this page draw on these open sources:

  • GBIFCC-BY 4.0occurrence records behind the range map, elevation, and record counts
  • iNaturalistCC0 / CC-BY / CC-BY-SAobservations, photos, and audio recordings
  • IUCN Red Listattributed factthe global conservation status
  • USGS NASpublic domainnative / introduced status
  • Natural Earthpublic domainthe relief basemap
  • USFSpublic domainnational-forest boundaries
  • USGS Protected Areas Databasepublic domainthe named parks, forests, and refuges behind "notable places to look"