About Mustela altaica Pallas, 1811
This species, known as both the Altai weasel and the mountain weasel, has slight sexual dimorphism. For males, head-to-tail-base body length is around 8.5–11 inches (220–280 mm), tail length adds 4–6 inches (100–150 mm), and weight ranges from 8–12 ounces (230–340 g). Females are slightly smaller, with a head-to-tail-base body length of around 8.5–10 inches (220–250 mm), a tail length of 3.5–5 inches (89–127 mm), and a weight of 4–8 ounces (110–230 g). This species molts seasonally in spring and autumn. Its summer coat is gray to gray-brown with patches of light yellow, while the winter coat is predominantly dark yellow with some brown. In both seasonal coats, the underbelly is pale yellow to creamy white. The upper section of the head between the muzzle and ears is usually a darker gray-brown. The tail is often more rufous than the back. The lips are white, and the chin has grayish-brown vibrissae. Altai weasels are generally solitary except during the mating season. Their specific mating system has not been confirmed, but other species in the same genus are polygynous, a system that typically includes one male and multiple females. This species breeds once per year. Males fight aggressively to gain access to females, and mating usually takes place in February or March, with young typically born in May. The gestation period lasts 30–49 days, but gestation timing and birth date can shift because females are capable of delayed implantation: after breeding and fertilization, the egg does not attach to the uterine endometrium to resume pregnancy until environmental resources are sufficient to support the pregnancy and feed the offspring after birth. Litter size ranges from one to eight young. Offspring are born altricial: they are dependent on their mother for nourishment, their eyes are closed at birth, and their fur is not well developed. Lactation lasts approximately two months. After weaning, young become independent but stay with their littermates until fall. Juveniles reach breeding age the following season, when they are just under one year old. Mountain weasels are strict carnivores, unlike many other caniforms which are omnivorous. Their diet primarily consists of pikas and voles, and they play an important ecological role in reducing or limiting the population sizes of these rodent species. They also eat muskrats, rabbits, ground squirrels, small birds, lizards, frogs, fish, and insects.
