After the eyes and ears open, from the fourth week onward, nearly always in the females first, the behavior of the young weasels changes as they begin to perceive the world around them. Within a few days they are actively exploring outside the den, and the mother no longer attempts to keep them all together. They are still a bit wobbly on their feet at first, especially the hind feet, but they can run along at least as quickly as mice.
By about the fifth week of age the young depend much more on the animal prey supplied by their mother than on her milk, and in the wild will soon be weaned. (Captive young ones may continue to suckle for as long as the mother will let them.) The appetites of young weasels are stupendous—each one is soon eating 20% to 40% of its own body weight per day (Sanderson 1949). Their mother may have a struggle to provide such largesse, even though breeding females can increase their hunting effort up to fourfold (Erlinge 1979a). Consequently, there is plenty of incentive for the young, as soon as they attain sufficient coordination, to start providing for themselves.
The milk teeth are usable for chewing on carcasses as soon as the deciduous carnassials (the third upper premolars and the fourth lower premolars; Chapter 2) have erupted. These appear at around the third week, and are replaced by the permanent teeth a couple of months later. Both sets of teeth erupt in a predictable sequence. The permanent carnassials, the fourth upper premolars and the first lower molars, are last in place (Hall 1951).
Killing behavior does not have to be learned, and, although the first attempts are clumsy, the young quickly improve with practice. Some observers maintain that the mother will bring a live but disabled rodent to the den and use it to teach killing technique to the young. We doubt this, since the hunting methods of weasels do not include any complex acquired skills (as in, say, the big cats and wolves), and the family life of weasels is too brief to give the young much chance to improve their proficiency under instruction. Besides, young that have been separated from their mothers at early ages are soon as expert as any others. Of course, the young of nearly all carnivores play with their littermates and with their prey, developing the crafts of their trade, but incidental learning through play is not the same thing as the mother deliberately teaching them.
Within another few weeks the young are more or less fully mobile and their motor coordination is improving daily. Standing up on their hind legs and jump ing over obstacles are among the last of the typical weasel skills to develop. By this time the young are fully furred and able to maintain their own body temperatures, at first only inside the den but later also outside it. They follow their mother on short hunting expeditions, dodging from one hiding place to another. If one falls behind it will call loudly with the infantile begging cry. The mother answers by trilling to show the lost one where she is, or, if necessary, she goes back to pick it up. At any potentially dangerous disturbance the mother hisses furiously, which causes the young to "freeze" and keep under cover.
The mother is totally fearless while she has young, and will perform feats of amazing courage, threatening any animal, however large, that gets in her way. Human observers, if unobtrusive, are simply ignored. Michael Hitchcock (p. 221) also reported that he was, on another occasion, standing by a hedge when he heard loud, high-pitched squeaking coming closer. Eventually a family of common weasels appeared, but he could not count the number of young as they were moving about so fast. Some of them actually ran over his boot. Gamekeepers also sometimes see a family of common weasels forming what looks like a "rope", or even "a string of chipolatas"—formed from a parent and a group of young in single file.
Galen Burrell (quoted by Hirschi 1985) watched one mother stoat with her family of young in the alpine meadows of the Colorado Rocky Mountains:
Grasping the plump vole in her mouth, she carried it about 100 m to the far corner of the rock pile.. .. Here she was greeted by eight young stoats. The nearly full-grown youngsters, mewing and chirping softly, excitedly sniffed their mother, one another, and then the breakfast vole. The stoat family disappeared into their burrow. . . . I . .. waited. .. . The mother reappeared. Standing on her hind legs she first scanned the surroundings, ignoring me, and then chirped. Eight heads popped out of the burrow. In a rushing stream of bodies the young ones followed their mother down the mountainside. . . . They would suddenly pile up behind an obstacle—usually a rock that was just too big for them to leap over. . .. She was forever returning to pick up stragglers. Grasping each one by its neck, she would drag it back to its brothers and sisters. Then the entire family would move on.. . . [They reached] a safe new hiding place.. .. Without pausing to rest she slipped away. [She killed a pika] 50 m away from her young ones. With a tremendous effort she dragged, pushed and sometimes carried the pika (which was twice her size) a short way towards [them, then] she pushed the pika under a rock. Then she headed up the slope towards the place she had hidden [a deer mouse killed earlier the same day]. Despite the time that had passed, she remembered exactly where the mouse was, picked it up and carried it back to her hungry children. Not long after that the mother stoat moved her brood up to where she had stashed the pika. Darkness fell as the family consumed their meal under the cover of their rock fortress. . . .
This extraordinary account gives a vivid picture of the flexibility of behavior that allows a mother weasel to make choices according to circumstances (e.g., to bring the young to the kill if the kill is too heavy to carry to them). It also underlines the energy invested by the mother in her young, and the enormous commitment of time and effort it takes for her to rear them alone.
Nor is this a unique observation. Sandell (1988) radio tracked a female stoat moving her young from one den to another and rushing around incessantly to provide enough food for them. Female stoats hunt with feverish intensity, and in one case related by Sandell, a female stoat with young ruined a colleague's radio-tracking study of watervoles by killing 15 to 20 voles in less than 2 days. The unfortunate vole researcher "found all of her transmitters in a heap of half-eaten voles. I was excited by this unequivocal proof of a stoat's hunting efficiency; curiously, my colleague wasn't as enthusiastic" (Sandell 1988).
In the wild, family parties of three to six or more stoats and longtails may be seen moving about together in early summer, most often in June and July. As the young get older, they scamper about, chasing each other and making high-pitched squeaking and whistling noises. One eyewitness account described seeing, from a distance of only 4 m, a group of five running across the ground. They included an adult with four young almost as big, running in concert, the adult in front. They "flowed along as if a single animal, accompanied by a wonderfully soft, fluty chirruping . .." (Ewan Young, personal communication). Usually only one adult is seen with a group of young, presumably the mother, but there are records of family parties accompanied by two adults. We suspect that the second "adult" may be a large young male (maybe a male with only female siblings) or possibly, in longtails, an adult male looking for mates.
By the time the young have hunted together for 2 or 3 weeks, they have their permanent teeth and some experience in using them, and they are ready to set out on their own. Families kept together in captivity have to be separated at this stage, as the young and the mother become increasingly intolerant and irritable with each other.
In New Zealand, as almost everywhere, stoats are distinctive enough to be noticed and rare enough to be remembered by casual observers. In places where many observers aggregate, such as national parks during the summer vacations, this would add up to a lot of information if only it could be organized.
One study done in 1976-1978 attempted to harness this resource and make some sense of it. It involved a simple reporting system whereby visitors to national parks in New Zealand sent in a prepaid record card for every stoat or group of stoats they saw (King 1982). The visitors reported seeing stoats in groups only in late spring and summer (from October to February in New Zealand), most often in December and January. This neatly confirmed what we already knew from trapping studies: Young stoats were seldom caught in any numbers before December, and were most numerous in January when the families break up and the young disperse. Erlinge (1977b) observed the same at the equivalent season (June) in Sweden.
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