Reproduction and development In the Northern Hemisphere, mating occurs in the April–July period. In spring, the male's
testes are enlarged, a process accompanied by an increase of
testosterone concentration in the
plasma.
Spermatogenesis occurs in December, and the males are fertile from May to August, after which the testes regress. Female stoats are usually only
in heat for a brief period, which is triggered by changes in day length.
Copulation can last as long as 1 hour. Stoats are not
monogamous, with litters often being of mixed paternity. Stoats undergo
embryonic diapause, meaning that the embryo does not immediately implant in the uterus after fertilization, but rather lies dormant for a period of nine to ten months. The
gestation period is therefore variable but typically around 300 days, and after mating in the summer, the offspring will not be born until the following spring – adult female stoats spend almost all their lives either pregnant or in heat. Males play no part in rearing the young, which are born blind, deaf, toothless and covered in fine white or pinkish down. The
milk teeth erupt after three weeks, and solid food is eaten after four weeks. The eyes open after five to six weeks, with the black tail-tip appearing a week later.
Lactation ends after 12 weeks. Prior to the age of five to seven weeks, kits have poor
thermoregulation, so they huddle for warmth when the mother is absent. Males become sexually mature at 10–11 months, while females are sexually mature at the age of 2–3 weeks whilst still blind, deaf and hairless, and are usually mated with adult males before being
weaned.
Territorial and sheltering behaviour Stoat territoriality has a generally mustelid spacing pattern, with male territories encompassing smaller female territories, which they defend from other males. The size of the territory and the ranging behaviour of its occupants varies seasonally, depending on the abundance of food and mates. During the breeding season, the ranges of females remain unchanged, while males either become roamers, strayers or transients. Dominant older males have territories 50 times larger than those of younger, socially inferior males. Both sexes
mark their territories with
urine,
feces and two types of
scent marks; anal drags are meant to convey territorial occupancy, and body rubbing is associated with agonistic encounters. The stoat does not dig its own burrows, instead using the burrows and nest chambers of the rodents it kills. The skins and underfur of rodent prey are used to line the nest chamber. The nest chamber is sometimes located in seemingly unsuitable places, such as among logs piled against the walls of houses. The stoat also inhabits old and rotting stumps, under tree roots, in heaps of brushwood, haystacks, in bog hummocks, in the cracks of vacant mud buildings, in rock piles, rock clefts, and even in
magpie nests. Males and females typically live apart, but close to each other. Each stoat has several dens dispersed within its range. A single den has several galleries, mainly within of the surface.
Diet As with the
least weasel, mouse-like rodents predominate in the stoat's diet. It regularly preys on larger rodent and
lagomorph species, and takes individuals far larger than itself. In Russia, its prey includes rodents and lagomorphs such as
European water voles,
common hamsters,
pikas and others, which it overpowers in their burrows. Prey species of secondary importance include small
birds,
fish, and
shrews and, more rarely,
amphibians,
lizards, and
insects. It also preys on
lemmings. In Great Britain,
European rabbits are an important food source, with the frequency in which stoats prey on them having increased between the 1960s and mid 1990s since the end of the
myxomatosis epidemic. Typically, male stoats prey on rabbits more frequently than females do, which depend to a greater extent on smaller rodent species. British stoats rarely kill shrews,
rats,
squirrels and water voles, though rats may be an important food source locally. In Ireland, shrews and rats are frequently eaten. In mainland Europe, water voles make up a large portion of the stoat's diet.
Hares are sometimes taken, but are usually young specimens. In New Zealand, the stoat feeds principally on birds, including the rare
kiwi,
kaka,
mohua,
yellow-crowned parakeet, and
New Zealand dotterel. Cases are known of stoats preying on young
muskrats. The stoat typically eats about of food a day, which is equivalent to 25% of the animal's live weight. The stoat is an opportunistic predator that moves rapidly and checks every available burrow or crevice for food. Because of their larger size, male stoats are less successful than females in pursuing rodents far into tunnels. Stoats regularly climb trees to gain access to birds' nests, and are common raiders of nest boxes, particularly those of large species. The stoat reputedly mesmerises prey such as rabbits by a "dance" (sometimes called the
weasel war dance), though this behaviour could be linked to
Skrjabingylus infections. Small prey typically die instantly from a bite to the back of the neck, while larger prey, such as rabbits, typically die of
shock, as the stoat's canine teeth are too short to reach the spinal column or major arteries. Additionally, a wide range of
birds of prey can take stoats, from small
northern hawk-owls (
Surnia ulula) and
short-eared owls (
Asio flammeus) to various
buzzards,
kites,
goshawks, and even
Eurasian eagle-owls (
Bubo bubo) and
golden eagles (
Aquila chrysaetos). Although not classified as birds of prey,
grey herons (
Ardea cinerea) are known to prey on stoats.
Diseases and parasites Tuberculosis has been recorded in stoats inhabiting the former Soviet Union and New Zealand. They are largely resistant to
tularemia, but are reputed to suffer from
canine distemper in captivity. Symptoms of
mange have also been recorded. Stoats are vulnerable to
ectoparasites associated with their prey and the nests of other animals on which they do not prey. The
louse Trichodectes erminea is recorded in stoats living in Canada, Ireland and New Zealand. In continental Europe, 26
flea species are recorded to infest stoats, including
Rhadinospylla pentacantha,
Megabothris rectangulatus,
Orchopeas howardi,
Spilopsyllus ciniculus,
Ctenophthalamus nobilis,
Dasypsyllus gallinulae,
Nosopsyllus fasciatus,
Leptospylla segnis,
Ceratophyllus gallinae,
Parapsyllus n. nestoris,
Amphipsylla kuznetzovi and
Ctenopsyllus bidentatus.
Tick species known to infest stoats are
Ixodes canisuga,
I. hexagonus,
I. ricinus and
Haemaphysalis longicornis. Louse species known to infest stoats include
Mysidea picae and
Polyplax spinulosa.
Mite species known to infest stoats include
Neotrombicula autumnalis,
Demodex erminae,
Eulaelaps stabulans,
Gymnolaelaps annectans,
Hypoaspis nidicorva, and
Listrophorus mustelae. The
nematode Skrjabingylus nasicola is particularly threatening to stoats, as it erodes the bones of the
nasal sinuses and decreases fertility. Other nematode species known to infect stoats include
Capillaria putorii,
Molineus patens and
Strongyloides martes.
Cestode species known to infect stoats include
Taenia tenuicollis,
Mesocestoides lineatus and rarely
Acanthocephala. ==In culture==