Mating Behavior In Adults

Mating is a very vigorous affair in all weasels. It has to be, because the stimulus of copulation is needed before ova can be released. All attempts to stimulate ovulation by injection of gonadotropins, the hormones that usually have this effect in other animals, have failed (Rowlands 1972; Gulamhusein & Thawley 1974), and the ovaries of unmated females have no corpora lutea.

Females are subordinate to males for most of the year, and normally avoid them, but a female is well able to reject unwanted suitors with displays of ferocious aggression. Only when she reaches full estrus will she accept a male's advances. He approaches cautiously, rubbing himself on the ground with twisting movements and making excited trilling calls. If she answers in kind, the brief courtship begins. They sniff at each other, trilling incessantly, and follow each other around. If she is fully receptive, or if it is not the first encounter between the pair, she may leap playfully around him, whereupon he immediately grabs her by the scruff of the neck (Figure 9.3). First encounters require somewhat more lively negotiation before getting to this stage, but the result is the same.

Figure 9.3 Stoats mating. The male holds the female firmly by the neck with a bite that may be locked, avoiding both release of the female and injury to the female. Ovulation in weasels is induced by copulation, so a female must be well stimulated. The baculum enables a male to maintain the extended and vigorous intromission required. Copulation is prolonged and may last a quarter hour to several hours.

Figure 9.3 Stoats mating. The male holds the female firmly by the neck with a bite that may be locked, avoiding both release of the female and injury to the female. Ovulation in weasels is induced by copulation, so a female must be well stimulated. The baculum enables a male to maintain the extended and vigorous intromission required. Copulation is prolonged and may last a quarter hour to several hours.

He drags her about, never letting go of her neck with his teeth (DonCarlos et al. 1986). Indeed, in the domestic ferret his bite becomes locked on her neck, which means that he cannot bite her too hard (Ewer 1973). She may break loose from the leg grasp, but not from the neck hold. She remains limp and passive while being carried, in a condition called tragschlaffe ("carry-sleep") by German observers. Young weasels behave in the same way when being carried from one den to another by their mother.

The male then grasps the female round the chest with his front legs, and arches his supple back to make pelvic thrusts, usually while both are lying on their sides. The baculum ensures that she is well stimulated, and that intromissions can be energetic, prolonged (usually about 15 minutes, but they can last several hours, with alternate periods of thrusting and resting), and frequent (up to several times per hour). Afterward the partners may rest, together or separately, and may repeat the procedure over the next 2 or 3 days, even though a single mating with intromission is usually enough to stimulate the release of luteinizing hormone (LH), which causes ovulation (Murphy 1989).

A female has no noble ideas about loyalty to one partner, however, and may accept other males she meets during her short receptive period. Mustelid sperm survive for much longer than those of most mammals, so the result can be litters with more than one father. Holland and Gleeson (2005) observed the genotype profiles of six wild-caught adult females and their prenatal offspring; one litter had been fathered by at least three males. Indeed, for captive breeding programs, Wright (1948) advocated introducing several different males to an estrous female one after another, until her heat subsides, as a means of ensuring success. But since a female does not ovulate until the second or third day after mating, the males that meet her on those days have more chance of fathering her litter than the first male (Amstislavsky & Ternovskaya 2000).

Mating success is all-important to a male. Since he takes no part in rearing his young, fathering many litters is a male's best passport to representation in the next generation (Chapter 14). So, each male attempts to find as many mates as possible each season, and the best way to do that depends on his age and social status (Chapter 8). But for a female, mating is only a dangerous preliminary to the real business, the rearing of the young, and as soon as her short period of heat is over she rejects all males with squeals and savage bites. There is no pair bond of any kind—indeed, the adults appear to have as little to do with each other as possible except when mating.

Even in captivity, where mating encounters can be set up in decent isolation from the possibility of interference from other males, some individual males are consistently uninterested or ineffective in achieving matings and others equally consistently successful (DonCarlos et al. 1986; Sundell 2003). Likewise, Müller (1970) found that some captive female stoats rejected all males, refusing to mate at all, and even the willing females did not necessarily accept all males offered as partners. Of 100 captive matings of least weasels, only 65% led to successful pregnancies. Individual mating success ranged from 0% to 33% in males, and from 0% to 50% in females (Sundell 2003). Breeding weasels is, therefore, an unpredictable business.

Well before her young are due, a mother weasel must find a safe, warm nest for them. She does not make one of her own, since weasels do not burrow, but then, she does not need to. It is a simple matter to find a ready-made nest, and if the owner is still at home it may find itself unwillingly providing board as well as lodging for the weasel family.

The best dens are the ones made by an animal of the right size. Small rodents make good dens for least weasels, but stoats and longtails look for a den made by larger rodents or rabbits. The den needs to be safe from any danger of flooding and thickly insulated with dry grass and leaves. The mother often improves the lining with fur plucked from dead prey; she does not take fur from her own belly, as a doe rabbit will. Nests built under good cover, such as in piles of rocks or logs, are especially attractive since they are safe from the prying paws of larger predators. When she has found a den, the mother weasel collects a store of food and then retires to await the birth (see Figure 14.2).

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