(subspecies: California weasel, Mustela f. xanthogenys)
The long-tailed weasel has a total length of 300-350mm and a tail comprising 40-70% of the head and body length. In most populations, females are 10-15% smaller than males. The eyes are black in daylight, but glow bright emerald green when caught in a spotlight at night. The dorsal fur is brown in summer, while the under parts are whitish and tinged with yellowish or buffy brown from the chin to the inguinal region. The tail has a distinct black tip. Long-tailed weasels in the southwestern US may have facial markings of a white or yellowish color. The long-tailed weasel moults twice annually, once in autumn (October to mid-November) and once in spring (March-April). Each moult takes about 3-4 weeks and is governed by day length and mediated by the pituitary gland. The long-tailed weasel has well developed anal scent glands, which produce a strong and musky odor. The long-tailed weasel drags and rubs its body over surfaces in order to leave the scent, to mark their territory and when started or threatened, to discourage predators.
The long-tailed weasel dens in ground burrows, under stumps or beneath rock piles. It usually does not dig its own burrows, but commonly uses abandoned ground squirrel holes. The nest chamber is lined with grass and leaves and the fur of prey.
The long-tailed weasel is a fearless and aggressive hunter which may attack animals far larger than itself. When stalking, it waves its head from side to side in order to pick up the scent of its prey. It hunts small prey, such as mice, by rushing at them and kills them with one bite to the head. With large prey, such as rabbits, the long-tailed weasel strikes quickly, taking its prey off guard. It grabs the nearest part of the animal and climbs upon its body, maintaining its hold with its feet. The long-tailed weasel then maneuvers itself to inflict a lethal bite to the neck.
The long-tailed weasel is an obligate carnivore which prefers its prey to be fresh or alive, eating only the carrion stored within its burrows. Rodents are almost exclusively taken when they are available. Its primary prey consists of mice, rats, squirrels, chipmunks, shrews, moles and rabbits. Occasionally, it may eat small birds, bird eggs, reptiles, amphibians, fish, earthworms and some insects. It occasionally surplus kills, usually in spring when the kits are being fed, and again in autumn. Some of the surplus kills may be cached, but are usually left uneaten. Kits in captivity eat from ¼ – ½ of their body weight in 24 hours, while adults eat only 1/5 – 1/3. After killing its prey, the long-tailed weasel laps up the blood, but does not suck it, as is popularly believed. With small prey, the fur, feathers, flesh and bones are consumed, but from large prey, only some flesh is eaten. When stealing eggs, the long-tailed weasel removes each egg from its nest one at a time, then carries it in its mouth to a safe location where it bites off the top and licks out the contents.
The long-tailed weasel is a solitary animal, except during mating season. It is most active in the night, but it also comes out in the day. Occasionally it can be seen hunting in the rocks near the outlet of the pond. The long-tailed weasel can climb trees and is a good swimmer. It uses lots of different vocalizations including squeals, squeaks, trills and purrs. It also releases a strong smelling musk during mating season and when it is frightened. It is very aggressive when its territory is invaded.
The long-tailed weasel mates in July-August. Litter size generally consists of 5-8 kits, which are born in April-May. The kits are born partially naked, blind and weighting 3 grams, about the same weight of a hummingbird. The long-tailed weasel’s growth rate is rapid, as by the age of 3 weeks, the kits are well furred, can crawl outside the nest and eat meat. At this time, the kits weigh 21-27 grams. At 5 weeks of age, the kit’s eyes open, and they become physically active and vocal. Weaning begins at this stage, with the kits emerging from the nest and accompanying the mother in hunting trips a week later. The kits are fully grown by autumn and by this time, the family disbands. The females are able to breed at 3-4 months of age, while males become sexually mature at 15-18 months.