Post by Super Communist on Oct 12, 2011 18:06:58 GMT -5
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Subfamily: Mustelinae
Genus: Mustela
Species: M. erminea
The stoat (Mustela erminea), also known as the ermine or short-tailed weasel, is a species of Mustelid native to Eurasia and North America, distinguished from the least weasel by its larger size and longer tail with a prominent black tip. Its range has expanded since the late 19th century to include New Zealand, where it is held responsible for declines in native bird populations. It is classed by the IUCN as Least Concern, due to its wide circumpolar distribution, and the fact that it does not face any significant threat to its survival. It is listed among the 100 "world's worst alien invasive species".
Etymology
The root word for "stoat" is likely either the Belgic word stout, meaning "bold" or the Gothic word stautan, meaning "to push". According to John Guillim, in his Display of Heraldrie, the word "ermine" is likely derived from Armenia, the nation where it was thought the species originated, though other authors have linked it to the Norman French from the Teutonic harmin (Anglo-Saxon hearma). This again seems to come from the Lithuanian word šarmu. In Ireland (where the least weasel does not occur), the stoat is referred to as "weasel", while in North America it is called "short-tailed weasel". A male stoat is called a dog, hob or jack, while a female is called a bitch or jill. The collective noun for stoats is either "gang" or "pack"
The stoat's direct ancestor was Mustela palerminea, a common carnivore in central and eastern Europe during the Middle Pleistocene, and probably reached North America in its current form during the late Blancan or early Irvingtonian. The stoat is the product of a process begun 5–7 million years ago, when northern forests were replaced by open grassland, thus prompting an explosive evolution of small, burrowing rodents. The stoat's ancestors were larger than the current form, and underwent a reduction in size to exploit the new food source. The stoat first arose in Eurasia, shortly after the long-tailed weasel arose as its mirror image in North America 2 million years ago. The stoat thrived during the Ice Age, as its small size and long body allowed it to easily operate beneath snow, as well as hunt in burrows. The stoat and the long tailed weasel remained separated until half a million years ago, when falling sea levels exposed the Bering land bridge.
Combined phylogenetic analyses indicate that the stoat's closest living relative is the mountain weasel (Mustela altaica), though it is also closely related to the least weasel (Mustela nivalis) and long-tailed weasel (Mustela frenata). Its next closest relatives are the New World Colombian weasel (Mustela felipei) and the Amazon weasel (Mustela africana).
Physical description
The stoat is entirely similar to the least weasel in general proportions, manner of posture and movement, though the tail is relatively longer, always exceeding a third of the body length,[20] though it is shorter than that of the long-tailed weasel. The stoat has an elongated neck, the head being set exceptionally far in front of the shoulders. The trunk is nearly cylindrical, and does not bulge at the abdomen. The greatest circumference of body is little more than half its length. The skull, although very similar to that of the least weasel, is relatively longer, with a narrower braincase. The projections of the skull and teeth are weakly developed, but stronger than those of the least weasel. The eyes are round, black and protrude slightly. The whiskers are brown or white in color, and very long. The ears are short, rounded and lie almost flattened against the skull. The claws are non-retractable, and are large in proportion to the digits. Each foot has five toes. The male stoat has a curved baculum with a proximal knob which increases in weight as it ages. Fat is deposited primarily along the spine and kidneys, then on gut mesenteries, under the limbs and around the shoulders. The stoat has 4 pairs of nipples, though they are only visible in females.
The dimensions of the stoat are variable, but not to the extent as the least weasel. Unusually among the Carnivora, the size of stoats tends to decrease proportionally with latitude, in contradiction to Bergmann's Rule. There is pronounced sexual dimorphism in size, with males being 1.5-2.0 times the weight of females. On average, males measure 187–325 mm in body length, while females measure 170–270 mm. The tail measures 75–120 mm in males and 65–106 mm in females. In males, the hind foot measures 40.0-48.2 mm, while in females it is 37.0-47.6 mm. The height of the ear measures 18.0-23.2 mm in males and 14.0-23.3 mm. The skulls of males measure 39.3-52.2 mm in length, while those of females measure 35.7-45.8 mm. Males weigh 258 grams, while females weigh less than 180 grams.
The stoat has large anal scent glands measuring 8.5 x 5 mm in males and smaller in females. The glands produce a strong musky odor produced by several sulphuric compounds. Scent glands are also present on the cheeks, belly and flanks. Epidermal secretions, which are deposited during body rubbing, are chemically distinct from the anal scent glands, which contain a higher proportion of volatile chemicals. When attacked or aggressive, the stoat excretes the contents of its anal glands, producing a strong, musky odour, which is distinct from that of least weasels.
Fur
The winter fur is very dense and silky, but quite closely lying and short, while the summer fur is rougher, shorter and sparse. In summer, the fur is sandy-brown on the back and head and a white below. The division between the dark back and the light belly is usually straight, though this trait is only present in 13.5% of Irish stoats. The stoat moults twice a year. In spring, the moult is slow, starting from the forehead across the back toward the belly. In autumn, the moult is quicker, progressing in reverse direction. The moult is initiated by photoperiod. The moult period starts earlier in autumn and later in spring at higher latitudes. In the stoat's northern range, it adopts a completely white coat (save for the black tail-tip) during the winter period. Differences in the winter and summer coats are less apparent in southern forms of the species. In the species' southern range, the coat remains brown, but is denser and sometimes paler than in summer.
Behavior
Reproduction and Development
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–August, after which the testes regress. Stoats are not monogamous, with litters often being of mixed paternity. The gestation period lasts circa 280 days. 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 3 weeks, and solid food is eaten after 4 weeks. The eyes open after 5–6 weeks, with the black tail-tip appearing a week later. Lactation ends after 12 weeks. Prior to the age of 5–7 weeks, kits have poor thermoregulation, thus the kits 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 behaviors
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, faeces and two types of scent marks; anal drags meant to convey territorial occupancy and body rubbing, which 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 30 cm of the surface.
Diet
As with the least weasel, mouse-like rodents predominate in the stoat's diet. However, unlike the least weasel which almost exclusively feeds on small voles, the stoat regularly preys on larger rodent and lagomorph species. In Russia, its prey includes rodents 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. 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 North America, where the ecological niche for rat and rabbit sized prey is taken by the larger long-tailed weasel, the stoat preys on mice, voles, shrews and young cottontails. 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 50 grams of food a day, which is equivalent to 25% of the animal's live weight.
The stoat is an opportunistic predator, which 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. The stoat regularly climbs trees to gain access to bird's nests, and are common raiders of nest boxes, particularly those of large species. The stoat reputedly immobilizes prey such as rabbits by mesmerizing them with a "dance", though this behaviour could be linked to Skrjabingylus infections. When tackling large prey, the stoat bites the nape of the neck whilst grasping it with its forefeet, intertwines its body around the animal then scratches its lower body with its back feet. Contrary to popular belief, blood which flows from resulting wounds is not sucked, but lapped up. The stoat may surplus kill when the opportunity arises, though excess prey is usually cached and eaten later to avoid obesity, as overweight stoats tend to be at a disadvantage when pursuing prey into their burrows. 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.
Communication
The stoat is a usually silent animal, but can produce a range of sounds similar to those of the least weasel. Kits produce a fine chirping noise. Adults trill excitedly before mating, and indicate submission through quiet trilling, whining and squealing. When nervous, the stoat hisses, and will intersperse this with sharp barks or shrieks and prolonged screeching when aggressive.
Aggressive behaviour in stoats is categorized in the following forms:
Non-contact approach, which is sometimes accompanied by a threat display and vocalization from the approached animal
Forward thrust, accompanied by a sharp shriek, which is usually done by stoats defending a nest or retreat site.
Nest occupation, when a stoat appropriates the nesting site of a weaker individual.
Kleptoparasitism, in which a dominant stoat appropriates the kill of a weaker one, usually after a fight.
Submissive stoats express their status by avoiding higher ranking animals, fleeing from them or making whining or squealing sounds.
Range and population
The stoat has a circumboreal range throughout North America, Europe, and Asia, from Greenland and the Canadian and Siberian Arctic islands south to about 35°N. Stoats in North America are found throughout Alaska and Canada south through most of the northern United States to central California, northern Arizona, northern New Mexico, Iowa, the Great Lakes region, Pennsylvania, and northern Virginia. The stoat in Europe is found as far south as 41ºN in Portugal, and inhabits most islands with the exception of Iceland, Svalbard, the Mediterranean islands and some small North Atlantic islands. In Japan, it is present in central mountains (northern and central Japan Alps) to northern part of Honshu (primarily above 1,200 m) and Hokkaido. Its vertical range is from sea level to 3,000 m.
Introduction to New Zealand
Stoats were introduced into New Zealand during the late 19th century in order to control rabbits and hares, but are now a major threat to the native bird population. The introduction of stoats was opposed by scientists in New Zealand and Britain, including the New Zealand ornithologist Walter Buller. The warnings were ignored and stoats began to be introduced from Britain in the 1880s, thus resulting in a noticeable decline in bird populations within six years. Stoats are a serious threat to ground and hole nesting birds, since they have very little means of escaping predation. The highest rates of stoat predation occur after seasonal gluts in southern beechmast seeds, which encourage the reproduction of rodents which stoats also feed on, thus encouraging stoats to increase their own numbers. For instance, the endangered takahe's wild population dropped by a third between 2006 and 2007, after a stoat plague triggered by the 2005–06 mast wiped out more than half the takahe in untrapped areas.
(Images and information, taken from Wikipedia)
