Editing Least weasel (section)

== Behaviour and ecology ==
===Reproduction and development===
The least weasel mates in April–July and there is a 34- to 37-day [[gestation period]]. In the [[Northern Hemisphere]], the average litter size consists of 6 kits and these reach [[sexual maturity]] in 3 to 4 months. Males may mate during their first year of life, though this is usually unsuccessful. They are [[fecund]] in February–October, though the early stages of [[spermatogenesis]] do occur throughout the winter months. [[Estrous cycle#Anestrus|Anestrus]] in females lasts from September until February.<ref name=h474>{{Harvnb|Harris|Yalden|2008|p=474}}</ref>

The female raises her kits without help from the male. They are {{cvt|1.5|to|4.5|g}} in weight at birth. Newborn kits are born pink, naked, blind and deaf, but gain a white coat of downy fur at the age of 4 days. At 10 days, the margin between the dark upper parts and light under parts becomes visible. The [[milk teeth]] erupt at 2 to 3 weeks of age, at which point the young start to eat solid food, though lactation can last 12 weeks. The eyes and ears open at 3 to 4 weeks of age, and by 8 weeks, killing behaviour is developed. The family breaks up after 9 to 12 weeks.<ref name=h474/> There is a single litter each year and least weasels can live for 7 or 8 years.<ref name=Collins/>

===Territorial and social behaviours===
[[File:Mustela nivalis (two, fighting).jpg|thumb|left|Two least weasels fighting]]
The least weasel has a typical mustelid territorial pattern, consisting of exclusive male ranges encompassing multiple female ranges. The population density of each territory depends greatly on food supply and reproductive success, thus the social structure and population density of any given territory is unstable and flexible.<ref>{{cite journal |author=Erlinge, S. |year=1974 |title=Distribution, territoriality and numbers of the Weasel ''Mustela nivalis'' in relation to prey abundance |journal=Oikos |volume=25 |issue=3 |pages=308–314 |jstor=3543948 |doi=10.2307/3543948 |bibcode=1974Oikos..25..308E}}</ref> Like the stoat, the male least weasel extends his range during spring or during food shortages. Its [[scent marking]] behaviour is similar to that of the stoat; it uses [[faeces]], [[urine]] and anal and dermal gland secretions, the latter two of which are deposited by anal dragging and body rubbing. The least weasel does not dig its own den, but nests in the abandoned burrow of another species such as a mole or rat.<ref name=h471>{{Harvnb|Harris|Yalden|2008|pp=471–472}}</ref> The burrow entrance measures about {{cvt|2.5|cm}} across and leads to the nest chamber located up to {{cvt|15|cm}} below ground. The nest chamber (which is used for sleeping, rearing kits and storing food) measures {{cvt|10|cm}} in diameter, and is lined with straw and the skins of the weasel's prey.<ref name=m277>{{Harvnb|Merritt|Matinko|1987|p=277}}</ref>

The least weasel has four basic vocalisations; a guttural hiss emitted when alarmed, which is interspersed with short screaming barks and shrieks when provoked. When defensive, it emits a shrill wail or squeal. During encounters between males and females or between a mother and kits, the least weasel emits a high-pitched trilling. The least weasel's way of expressing aggression is similar to that of the [[stoat]]. Dominant weasels exhibit lunges and shrieks during aggressive encounters, while subdominant weasels will emit submissive squeals.<ref name=h471/>

===Diet===
[[File:Donnola vs lepre.JPG|thumb|right|Taxidermy exhibit showing a least weasel attacking a [[European hare]], in the Natural History Museum of Genoa]]

The least weasel feeds predominantly on [[mouse]]-like [[rodent]]s, including [[mice]], [[hamster]]s, [[Gerbillinae|gerbil]]s and others. It usually does not attack adult hamsters and [[rat]]s. [[Frog]]s, [[fish]], small [[bird]]s and bird eggs are rarely eaten. It can deal with adult [[pika]]s and gerbils, but usually cannot overcome [[brown rat]]s and [[souslik]]s. Exceptional cases are known of least weasels killing prey far larger than themselves, such as [[capercaillie]], [[Hazel grouse|hazel hen]] and [[hare]]s.<ref name=s987>{{Harvnb|Heptner|Sludskii|2002|pp=987–988}}</ref> In England, a favoured prey item is the [[field vole]] (''Microtus agrestis''). These have fluctuations in population size, and in years of abundance may form up to 54% of the weasel's diet. In years of scarcity, birds form a greater proportion of the diet and female least weasels may fail to breed.<ref>{{cite journal |author=Tapper, S. |year=1979 |title=The effect of fluctuating Vole numbers (''Microtus agrestis'') on a population of Weasels (''Mustela nivalis'') on farmland |journal=Animal Ecology |volume=48 |issue=2 |pages=603–617 |jstor=4182 |doi=10.2307/4182 |bibcode=1979JAnEc..48..603T}}</ref>

Despite its small size, the least weasel is a fierce hunter, capable of killing a [[rabbit]] five to 10 times its own weight.<ref name=mac208>{{Harvnb|Macdonald|1992|p=208}}</ref> Although they are commonly taken, the rabbits are usually young specimens, and become an important food source during the spring, when small rodents are scarce and rabbit kits are plentiful. Male least weasels take a higher proportion of rabbits than females, as well as an overall greater variety of prey. This is linked to the fact that being larger, and having vaster territorial ranges than females, males have more opportunities to hunt a greater diversity of prey.<ref name=h472>{{Harvnb|Harris|Yalden|2008|pp=472–473}}</ref>

The least weasel forages undercover, to avoid being seen by foxes and birds of prey. It is adapted for pursuing its prey down tunnels, though it may also bolt prey from a burrow and kill it in the open.<ref name=h472/> The least weasel kills small prey, such as [[vole]]s, with a bite to the [[occiput|occipital]] region of the skull<ref name=s987/> or the neck, dislocating the [[cervical vertebrae]]. Large prey typically dies of [[blood loss]] or [[Shock (circulatory)|circulatory shock]].<ref name=h472/> When food is abundant, only a small portion of the prey is eaten, usually the [[brain]]. The average daily food intake is {{cvt|35|g}}, which is equivalent to 30–35% of the animal's body weight.<ref name=s987/>

===Predators and competitors===
[[File:Weaselsvsstoat.png|thumb|Least weasels driven from a [[mountain hare]] carcass by a [[stoat]], as illustrated in [[Gerald Edwin Hamilton Barrett-Hamilton|Barrett-Hamilton]]'s ''A History of British Mammals'']]
The least weasel is small enough to be preyed upon by a range of other predators.<ref name=h475>{{Harvnb|Harris|Yalden|2008|p=475}}</ref> Least weasel remains have been found in the excrement of [[red fox]]es, [[sable]]s, [[steppe polecat|steppe]] and [[European polecat|forest polecat]], [[stoat]]s, [[eagle owl]]s and [[buzzard]]s.<ref name=s992>{{Harvnb|Heptner|Sludskii|2002|p=992}}</ref> The [[owls]] most efficient at capturing least weasels are [[barn-owl|barn]], [[barred owl|barred]], and [[great horned owl]]s. Other birds of prey threatening to the least weasel include [[Broad-winged hawk|broad-winged]] and [[rough-legged buzzard]]s. Some [[snake]] species may prey on the least weasel, including the [[black rat snake]] and [[Agkistrodon contortrix|copperhead]].<ref name=m277/> Aside from its smaller size, the least weasel is more vulnerable to predation than the stoat because it lacks a black predator deflection mark on the tail.<ref name=h475/>

In areas where the least weasel is [[Sympatry|sympatric]] with the [[stoat]], the two species compete with each other for rodent prey. The weasel manages to avoid too much competition by living in more upland areas, feeding on smaller prey and being capable of entering smaller holes. It actively avoids encounters with stoats, though female weasels are less likely to stop foraging in the presence of stoats, perhaps because their smaller size allows them to quickly escape into holes.<ref name=h469>{{Harvnb|Harris|Yalden|2008|p=469}}</ref>

=== Diseases and parasites ===
[[Ectoparasite]]s known to infest weasels include the [[louse]] ''Trichodectes mustelae'' and the [[mite]]s ''[[Demodex]]'' and ''Psoregates mustela''. The species may catch [[flea]]s from the nests and burrows of its prey. Flea species known to infest weasels include ''Ctenophthalmus bisoctodentatus'' and ''Palaeopsylla m. minor'', which they get from moles, ''P. s. soricis'', which they get from shrews, ''Nosopsyllus fasciatus'', which they get from rodents and ''Dasypsyllus gallinulae'' which they get from birds.<ref name=h475/>

[[Helminth]]s known to infest weasels include the [[trematode]] ''[[Alaria (flatworm)|Alaria]]'', the [[nematode]]s ''[[Capillaria (nematode)|Capillaria]]'', ''Filaroides'' and ''[[Trichinella]]'' and the [[cestode]] ''[[Taenia (flatworm)|Taenia]]''.<ref name=h475/> Least weasels are commonly infected with the [[nematode]] ''[[Skrjabingylus nasicola]]'', adults of which are found in the nasal sinuses and can damage the skull. There is no evidence that this has serious detrimental effects on even heavily infested animals.<ref>{{cite journal |author=King, C. M. |year=1977 |title=The effects of the nematode parasite ''Skrjabingylus nasicola'' on British weasels (''Mustela nivalis'') |journal=Journal of Zoology |volume=182 |issue=2 |pages=225–249 |doi=10.1111/j.1469-7998.1977.tb04157.x}}</ref>