Field Guide/Mammals/Least Weasel
|Mustela nivalis (Least Weasel)|
Size: Total Length: 6.5-8 inches (16.51-20.32cm) Weight: 1-2 ounces (28-57g)
Description: The least weasel has a long and slender body with short limbs. It has a long neck and a narrow, flat head. It has round ears, large black eyes, and sharp claws on each of its feet. It's fur is normally brown but will turn all white during the winter in northern populations.
Similar Species: The least weasel is similar in appearance to the ermine and the domesticated ferret.
Range: Their range is the Nearctic and Palearctic regions.
Habitat: The least weasel can be found in open forests, farmlands, prairies, and meadows. They avoid open spaces.
Diet: The least weasel is primarily a carnivore. They feed mostly on small rodents. When rodents are scarce they will feed on bird eggs, nestlings, and small reptiles.
Activity: They are active during the day and during the night.
Reproduction: Males have more than one female mate at a time. Litters typically have 1 to 7 offspring. They reach sexual maturity at 4 to 8 months. Breeding can occur all year but typically occurs in Spring and late Summer.
Lifespan: The average lifespan is less than one year. Some may live for as many as 9 years.
Notes: The least weasel moves very quickly. They sometimes climb trees to investigate birds’ nests and are also able to swim slowly. They hunt at whichever time of day their prey is most abundant. Males and females live apart from each other aside from the breeding season. 
- Newell, T. (1999), "Mustela Nivalis", Animal Diversity, http://animaldiversity.ummz.umich.edu/accounts/Mustela_nivalis/, retrieved October 9, 2012
- Steven, S.; Carolyn, K. (1994), "Mustela nivalis", Mammalian Species: 1-10, http://www.science.smith.edu/msi/, retrieved October 9, 2012