Food habits of British stoats (Mustela ermined) and weasels (Mustela nivalis)

Information on the food habits of stoats and weasels was obtained chiefly from gut analyses of carcasses sent from various parts of Britain. Lagomorphs, small rodents and birds form the bulk of the food taken by these predators. The three food classes appear to be equally important to stoats, whereas weasels obtain nearly half of their food from small rodents. Microtus was the most important small rodent in the diet of both stoats and weasels. Game birds were taken more by stoats than weasels; the chief bird prey of the latter was passerines.     

Moult and colour change in English weasels (Mustela nivalis)

The moult pattern of the weasel is similar to that of the stoat ( M. erminea ). English weasels rarely turn white in winter but the winter fur is a paler shade of brown than the summer fur.     

The effects of the nematode parasite Skrjabingylus nasicola on British weasels (Mustela nivalis)

Adult worms of Skrjabingylus nasicola are found in the nasal sinuses of mustelids, and when numerous may cause considerable distortion of the frontal bones. A heavy infestation is commonly assumed to be detrimental to the individual and possibly also to the population. To examine this belief, the frequency of occurrence ("incidence") and extent of damage caused by S. nasicola were analysed with respect to the climate of seven sample areas and the age, sex and body size of 614 British weasels. Incidence ranged from 69–100% of the sample, and mean skull damage from 31 to 53 on an index scale of 0–8 points. Significant correlations were found between incidence and date of collection of young weasels, and between extent of damage and mean number of rain-days in the area. Male weasels were more badly damaged than females, though incidence was the same in both sexes. There was no evidence that badly damaged weasels were smaller, lighter, leaner or died sooner than lightly or undamaged ones, nor that, in the wild, they were infested by eating shrews.     

The stoat Mustela erminea population decline in northern Belarus and its consequences for weasels Mustela nivalis

Abstract

In northern Belarus, we have documented a decline in the local stoat Mustela erminea population following the naturalisation of the American mink Mustela vison. The most likely cause is the reduction in the density and distribution of the main prey of stoats, the riparian voles (the water vole Arvicola terrestris and the root vole Microtus oeconomus), due to excessive predation by mink. Since the stoat population has declined, the number of weasels Mustela nivalis in marshlands has increased and their mean body mass has increased, correlated with the higher number and mean weights of rodents available for weasels in marshland compared with forest habitats.     

The diet of weasels (Mustela nivalis vulgaris) from Purerua Peninsula,Bay of Islands,New Zealand

We studied the diet of weasels (Mustela nivalis vulgaris) caught on Purerua Peninsula, Bay of Islands, by examining gut contents of 16 individuals caught between 2011 and 2012. Mammals were the prey group most consumed by weasels, when measured both as frequency of occurrence and dry weight. In addition, weasels consumed introduced birds, native invertebrates and reptiles, including the endemic copper skink (Oligosoma aeneum), supporting previous studies and suggesting that weasels have greater effects on biodiversity losses than previously acknowledged.     

The food of feral mink (Mustela vison) in Scotland

Feral American mink ( Mustela vison ) thrive in Scotland. The potential impact of the mink on the native fauna was investigated through its food. Fifty-five stomachs and 33 scats were analysed by identifying the indigestible remains. Fish formed the main prey (49% occurrence) and birds and mammals 28% and 23% respectively. Most of the fish eaten were Salmonidae (brown trout and salmon). No remains of eels were found.
Mink may compete with otters for food, but the smaller prey taken by the mink and its greater use of land separates it from the otter. Mink seem to be occupying a vacant feeding niche in Scotland.     

Effect of the odour of weasels (Mustela nivalis L.) on trapped samples of their prey

Summary The presence of weasel anal gland secretion on rodent live traps substantially depresses population estimate by greatly reducing the catch of Microtus agrestis. The catch of Apodemus sylvaticus remains almost unaffected.     

Climate and refugial origin influence the mitochondrial lineage distribution of weasels (Mustela nivalis) in a phylogeographic suture zone

Overarching trends can be seen in European mammalian phylogeography, yet it is clear that species responded differently depending on adaptations to past environments. We built upon previous work on the phylogeography of weasels (Mustela nivalis) in Europe by using well‐preserved museum specimens from a proposed phylogeographic suture zone. The complete cytochrome b gene was amplified from 49 individuals from present‐day Poland and analyzed with previously published data on a European scale to identify glacial refugia and infer recolonization processes. Bayesian coalescent analysis revealed the importance of the Last Glacial Maximum and the Younger Dryas in the diversification of, and demographic changes in, identified mitochondrial lineages. Our analysis, in conjunction with the available fossil data, strongly points to a Carpathian origin for one of the lineages, and further highlights the importance of this region as a refugium for European mammals. Mustela nivalis originating from this refugium appear to have a selective advantage over M. nivalis from other lineages in certain environments in the suture zone in central Europe, with climate clearly influencing the distribution of mitochondrial DNA lineages. This has important implications not only for our understanding of how past climatic events shaped the genetic architecture of species, but also how they will respond to current and future climatic changes. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 57–69.     

On co-existence,foraging strategy and the biogeography of weasels and stoats (Mustela nivalis and M. erminea) in Britain

Summary Mustela nivalis and M. erminea, two sympatric species of weasels of superficially similar appearance and habits, have different breeding and foraging strategies associated with the difference in their body size. M. nivalis is more efficient in exploiting small rodent prey, and can breed rapidly to take immediate advantage of rodent peaks, but is vulnerable to local extinction during rodent declines. M. erminea has more generalized food habits, and is the larger and probably the dominant species, but is limited by delayed implantation to producing only one litter a year. M. nivalis is therefore superior in exploitation competition, and erminea in interference competition. We offer the hypothesis that the co-existence of the two species is permitted by a balance of these competitive advantages determined, at a given time or place, by the heterogeneity of the environment and the distribution of the prey fauna. We use this hypothesis to explain cases where co-existence has either broken down or is not recorded (the results of simultaneous introductions to New Zealand and Terschelling Island, and of myxomatosis in Britain, and the distribution of nivalis and Erminea on the offshore islands of Britain). We argue that the diversity and size distribution of the prey fauna of an island (which are both related to its area and isolation) are important in deciding the species and size of mustelids surviving there; for example, we suggest that nivalis was present in Ireland in immediate post-glacial times but became extinct with the lemmings.     

The weasel (Mustela nivalis) helps in detectingDemodex mites in rodents

Many stages of parasites living in or on prey animals can pass undestroyed through the intestinal tract of carnivores and carnivorous animals. Nematode eggs, whole nematodes, even cestodes can be found in their faeces, but of the ectoparasitic mites usually only the eggs are found. It was therefore surprising thatDemodex mites, some of them even still alive, were found to have been passed by a captive weasel.Members of the genusDemodex cannot be detected by routine procedures yielding ectoparasites. Most species do not give rise to pathological alterations and the site they inhabit may not be known. To isolate them, either the skin complex or the organ supposed to containDemodex has to be digested with KOH or else the mites have to be squeezed out of the follicles. Compared to this, the weasel method is very simple.Faecal pellets (not more than one or two) are carefully ground with a mortar in a saturated ZnSO₄ solution and poured through a fine mesh into a test tube so as to form a little mountain at the orifice. The tube is allowed to stand for 25–30 min. Due to their lower specific weight, protozoan oocysts, worm and mite eggs and the specimens ofDemodex rise to the surface. The meniscus is then touched with a cover slip and, with the adhering drop, is placed on a slide. In the case of the parasites mentioned here, the procedure can be repeated once more after 5 min. Demodex mites and all their developmental stages, including the eggs, appear in a clean preparation on the slide, ready to be measured, drawn, or photographed. The mites are in excellent shape. Some of them even move their gnathosome and legs, if fresh faeces are submitted to the concentration technique; the method is very quick, with results being obtained within 30 min. Although only one rodent can be fed to a weasel per day, it takes a minimum of labour to examine the faeces, which can also be stored in a refrigerator.As the weasel was young when caught, it was not restricted in its feeding habits to the common vole (Microtus arvalis) which is its main prey in Middle Europe, but took other rodents, too. This proved to be very helpful when two different rodent species were to be tested forDemodex. In order not to mix them up, a white mouse of aDemodex-free stock was given on the day between. By this it was also possible to make a semi-quantitative survey of theDemodex population size of one host animal, because the faecal pellets of a weasel are very small and can be entirely used. All available rodents can be tested by this method. If the weasel is hungry it might even be possible to feed only the parts of the body of bigger host animals suspected to containDemodex.The disadvantages of the weasel method are that (a) no permanent mounts can be made, because the zinc sulfate (or any other saturated solution commonly used for these purposes) forms crystals when a mounting medium is added, and (b) the site inhabited by the mites has still to be ascertained; this is particularly important, since one host species can harbour more than oneDemodex species, and these may look very similar.     

Microsatellite markers for genetic studies in the weasel (Mustela nivalis)

This study reports the first set of microsatellite markers for the weasel (Mustela nivalis). We chose to isolate loci with tetranucleotide repeat motifs because they can be scored less ambiguously than the more commonly used dinucleotide loci. All 11 loci showed considerable variation within a population sample of 28 individuals from Portugal, with number of alleles ranging from four to nine per locus and observed and expected heterozygosities ranging from 0.21 to 0.86 and from 0.40 to 0.84, respectively. No linkage disequilibrium was detected between pairs of loci, and only one locus (Mn 1.30) deviated from Hardy–Weinberg equilibrium expectations in the analyzed population sample. Among the 11 loci, Mn 1.30 was the only one for which all known males were homozygous. Analysis of an additional population sample of 23 individuals (14 males and 9 females) from Denmark revealed that all males, but only four females, were homozygous for Mn 1.30, supporting the idea that the locus is X-linked. These novel polymorphic microsatellite markers should be useful in studies of population genetics and molecular ecology of the weasel.