Ermine

## Description

The ermine (Mustela erminea) is a mustelid native to Eurasia and the northern portions of North America. Introduced in the late 19th century into New Zealand to control rabbits, the ermine has had a devastating effect on native bird populations. It was nominated as one of the world's top 100 "worst invaders".

## Appearance

The ermine has an elongated neck, the head being set exceptionally far in front of the shoulders. The trunk is nearly cylindrical and does not bulge at the abdomen. The greatest circumference of the body is little more than half its length. The eyes are round, and black and protrude slightly. The whiskers are brown or white in color, and very long. The ears are short and rounded and lie almost flattened against the skull. The claws are not retractable and are large in proportion to the digits. Each foot has five toes. The winter fur is very dense and silky, but quite closely lying and short, while the summer fur is rougher, shorter, and sparse. In summer, the fur is sandy brown on the back and head and white below. The ermine molts twice a year. In its northern range, the ermine adopts a completely white coat (save for the black tail-tip) during the winter period. Differences in the winter and summer coats are less apparent in the southern forms of the species. In the species' southern range, the coat remains brown but is denser and sometimes paler than in summer.

## Distribution

Ermine are found across the northern subarctic, Arctic, and temperate regions of Asia, Europe, and North America. Across the New World, they are distributed from west to east in a wide belt running from the Arctic Ocean and nearby islands in the Canadian Archipelago south to the northern United States. They are not found on the Great Plains. These animals prefer riparian woodlands, shrubby fencerows, marshes, alpine meadows, and open areas near forests or shrub borders.

## Behavior

This species is largely crepuscular or nocturnal but is sometimes active during the day. Ermine are good climbers and they use trees when escaping predators, rest, and search for food. They are largely solitary. They are territorial and intolerant of other ermine in their range, particularly those of the same gender. Within their range, they typically use several dens, often those of their prey species. They usually travel alone, except when mating mothers with their older offspring. Adult males will dominate females and young. Females generally remain in the area of their birth throughout their lives. The males disperse and secure a large territory that usually encompasses or overlaps females' territories. This species maintains exclusive boundaries that they patrol and mark with scent. They have keen senses of sight, hearing, smell, and touch that help to locate prey.

## Diet

Ermine are carnivores and prey on small, warm-blooded vertebrates, particularly mammals the size of rabbits or smaller. When mammals are scarce, they eat birds, eggs, fish, frogs, and insects.

## Reproduction

Ermine are polygynandrous (promiscuous), with both males and females mating with multiple partners. They mate from late spring to early summer. Females bear 1 litter only per year. After a gestation of around 280 days, young are born during April or May. Gestation includes a period of developmental delay of 8 to 9 months. Litter sizes range from 3 to 18 and average from 4 to 9. Young grow quickly and can hunt with their mothers when 8 weeks old. Weaning takes place at around 10 weeks. Females reach adult size by about 6 weeks after birth and are able to mate at 60 to 70 days of age, often before being weaned. Males gain adult size during their second summer.

## Population

### Population threats

Potential threats include increasing access and unrestricted trapping by people, habitat fragmentation and loss, interactions with introduced species, as well as changes in prey availability. Generally, mustelids are very vulnerable to trapping, not only to traps that are set specifically for them. Ermine may be less threatened than other furbearers by habitat change from fire disturbances or timber harvest due to the preference for communities with early-successional stages and their aversion to dense forests. Clear-cut logging, however, may be a threat in Alaska, particularly in the unproductive, mid-successional regrowth forest areas which seem to be the favored habitat. Another concern is the loss of genetic integrity and the transmission of pathogens (like canine distemper) and parasites from native or introduced stocks of other carnivores.

### Population number

Ermine is an abundant species and it has a wide circumpolar distribution, but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List, and its numbers today remain stable.

### Ecological niche

Ermine are important predators of small mammal communities within the ecosystems where they live.

## Fun Facts

Ermine are very skillful tree climbers and are able to go down a trunk headfirst, as squirrels do.

Ermine move in a zigzag manner, and after each leap will bounce 20 inches from the ground. They can travel further than 9 miles in a night to find food.

Even though ermine inhabit areas with very cold winters, they are active during the entire year.

Although ermine are mostly terrestrial, they are able to climb trees and they swim well.

Ermine have a bad smell which serves to keep other ermine away.

At 7 weeks old, male babies are larger than their mothers.