Weasels

Weasels are members of the Mustelidae family, a group of carnivores that also includes badgers, otters, ferrets, martens, minks, and wolverines.  All species have long necks and bodies with short legs, small, round ears, and thick fur.  They are solitary animals that are active year-round, mostly at night.  They use strong smelling scents from anal glands to mark their territory and signal other individuals when seeking a mate. 

^{Clockwise: Black-footed ferret, Mustela nigripes, by J. Michael Lockhart, USFWS, Dec 2010; American mink, Neogale vison, by Patrick Reijnders; Common badger, Meles meles meles, by Prosthetic Head, Jun 2010; Wolverine, Gulo gulo, by National Park Service, 1968; Pine marten, Martes martes, by John Surrey, May 2015; Eurasian otter, Lutra lutra, by Bernard Landgraf, Jan 2005}

There are five species of weasels native to the Americas.  Short-tailed weasels, also-known-as stoats, Mustela erminea and least weasels, Mustela nivalis, are found in the Arctic regions of northern Canada and Alaska.  The long-tailed weasel, Mustela frenata, ranges from southern Canada through most of the continental United States to Central America and the northern areas of South America.  Two other species of weasels that live in northern and central South America include the Colombian weasel, Neogale felipei, and the Amazon weasel, Neogale africana.  The odd species name for the Amazon weasel was first derived from a museum skeleton that had been mislabeled as originating in Africa.

In summer, weasels are sandy-brown on their backs with light colored bellies and black-tipped tails.  Species found in far northern regions molt twice each year, when their fur, except for the tail, changes to white for the winter.  They have small heads with long whiskers and small, rounded ears.  Necks and bodies are long and slim with short legs.  Weasels are found in a variety of habitats from farmland to forested areas, but are often located along an open water source such as streams, rivers, and estuaries.  The Colombian weasel has partial webbing of its feet, suggesting a semi-aquatic lifestyle.  Long-tailed weasels and Amazon weasels have been observed easily swimming in larger bodies of water.

With their elongated bodies, weasels are able to easily follow prey into burrows, as well as through paths under ground cover such as leaves, snow and ice.  Weasels are carnivores, hunting small mammals, birds, insects, and crustaceans.  They are generally nocturnal hunters with keen senses of smell and hearing, making them capable predators.  The least weasel, with a body between five and ten inches in length, has more biting power than a lion or hyena.  A rabbit, its favorite prey, is five to ten times the size and weight of a weasel, but the weasel easily dispatches its prey by gripping the back of the neck to break the spine and kill it.  Weasels are excellent climbers, allowing them to pursue prey off the ground.

Weasel dens are built in burrows abandoned by other animals.  A nest of grass and leaves is lined with fur from their prey.  Mustelids use a reproductive strategy called embryonic diapause, found in very few mammal species.  After conception, the new embryo enters a phase where it remains dormant for a period of time before implanting itself in the uterine wall to begin growth and development.  The gestation period can be extended up to a year until conditions are optimal for the survival of both the offspring and the mother.  In long-tailed weasels mating takes place in mid to late summer, but babies are born the following spring, when temperatures are warmer and food resources are plentiful and readily available.

Weasels  mate in mid to late summer, and young are born the following spring.  Kits are blind and deaf for the first two to three weeks after being born, but grow quickly and are weaned between five and six weeks.  In most species, both males and females are sexually active before the end of their first summer.  In one species, the short-tailed weasel, living in northern areas with short summers, females are sexually mature at two to three weeks while still blind and deaf following birth.  Most are sexually mated before they are weaned.  Kits will leave the nest to claim their own territory before their first winter.

Most species worldwide are listed as of least concern, with strong populations.  An exception is the Colombian weasel, about which very little is known.  The first live one was discovered by an amateur naturalist in 2011.  There are fewer than a dozen documented animals living in riparian habitats in the cloud forests of Colombia above 5,000 feet.  It is thought they are doing well, but too little is known of this relatively new species.  The Jurica-Suchy Nature Museum or most local nature museums have wonderful displays of weasels and other members of the mustelid family for you to learn more.