Short-tailed Weasel
(Mustela erminea)

Observations in the Hylebos Wetland

by Ken Steffenson

In late July, FOWH supporters Mark and Adele Freeland were showing off the Wetlands to Mark’s sister from Colorado. Near the Deep Sinks they saw movement in the underbrush, and out came a short-tailed weasel (also called an ermine or stoat).

They then witnessed the weasel retrieve its prey — a freshly caught small rabbit.
“What a rare treat to see this critter in action,” Adele said.

One other sighting was reported recently in the Hylebos Wetlands, and Thais Bock saw what she was pretty sure was another short-tailed weasel, in early August at Saltwater State Park.

Appearance

This small weasel ranges in length from 7 3/8” to 13 5/8”, and the common name comes from the 2” to 4” long tail. They weigh an amazingly light 1 to 3 ounces.
They have long, slender, cylindrical bodies, short legs, and small, horizontally flattened heads that taper to a blunt nose. Their hairy ears are somewhat prominent, and the five toes on each foot are tipped with small but very sharp claws.

Their fur is usually brown or reddish brown on the upper parts, and white on the underparts from the chin to the crotch and on the inside of the hind legs. The tail is brown with a black tip.

In high elevations the fur of these animals turns white in winter, and the common name “ermine” is usually used for this appearance. When short-tailed weasels turn white, only the tip of the tail stays dark.

Taxonomy and Close Relatives

Kingdom: Animalia. Phylum: Chordata. Subphylum: Vertebrata. Class: Mammalia. Order: Carnivora (carnivores). Family: Mustelidae (mustelids). Subfamily: Mustelinae. Genus: Mustela. Species: erminea.

Close relatives found in North America include the least weasel (M. nivalis rixosa) and the long-tailed weasel (M. frenata). The family Mustelidae, made up of 67 species in 26 genera, also includes ferrets, badgers, polecats, skunks, martens, fishers, and otters.

Geographical Distribution and Habitat

Although members of Mustelidae are widespread from the tropics to the arctic and in the Americas, Africa, Eurasia, and introduced in New Zealand, the short-tailed weasel is native to only North America and Eurasia.

Short-tailed weasels are found throughout Washington state, with the exception of the Columbia Basin.

This small carnivore most often lives in forested and wooded areas. They seem to prefer staying close to protective cover, and seldom stray far from fallen trees or thick vegetation.

Ecological Lifestyle

Weasels are renowned for their fierceness and hunting prowess in comparison to their small size. Along with the European polecat, weasels are unusual because of their ability to catch and kill, single-handed, prey that is much larger than themselves.

Here are a few quotes I saw in books: “Tooth for tooth and ounce for ounce, the weasel is the fiercest and most efficient predator in the mammal world,” “… the fiercest mammal for their size,” and “… the most blood-thirsty animals in existence.” The last quote may refer to the weasels’ voracious feeding habits, eating up to 40 percent of their weight daily. They are also known to often kill more than they can eat. They prey mainly on small mammals such as baby rabbits, chipmunks, mice, voles, and shrews.

Short-tailed weasels hold their territories with marks of urine, feces, and scent-gland secretions. Within these territories they build a nest, usually appropriated from one of their victims. Nests are usually above ground, but sometimes below, and are always lined with the fur of prey that has been dragged into the nest to be eaten.

These weasels have an unusual reproductive process. Breeding takes place in July and August, eggs are fertilized and travel to the uterus while developing a bit into a ball of cells called a blastocyst. Then, instead of implanting to the uterus wall, the blastocysts float free and do not develop further. This delayed implantation lasts for up to ten months before the blastocyst finally implants to the uterus wall, development restarts, and a litter of four to thirteen (usually six or seven) is born in late April or early May.

The short-tailed weasel is an amazing mammal with fascinating traits. We’re lucky to have them in the Wetlands!

Ken Steffenson is a long-time member of the Friends of the Hylebos.