Species Of Weasels Research Articles

Scent lures and baits at camera traps improve time to first detection and detection probability of two typically elusive species of weasel

AbstractThere is a growing body of evidence that weasel species are in decline globally. More data on their ecology and distribution are needed to plan and justify any conservation management actions. Camera trapping can be an effective survey method for many species; however, the small size and quick movements of weasels present challenges in detection and little consensus exists on practices for attracting them to improve detection. This study tested different combinations of meat baits and scent and audio lures to assess the most effective methods. Camera traps were set up in clusters of three at 42 sites to test the effectiveness of these combinations, accounting for season, in terms of the time to first detection (TFD), detection probability using occupancy models, and the number and clarity of weasel photos. We also repeated TFD and detection probability analyses for setups that were ≥ 20 m apart in case of overlap of effects. The average TFD across all sites was 43 days. Fall typically had the shortest TFD with beaver bait in fall achieving the best results. After accounting for occupancy, predicted detection probability across a 60-day survey was highest in fall with the best combination being salmon lure and beaver bait. The treatment type did not impact the average number of photos captured, but the clarity of photos was significantly positively related to use of bait and lure, type of lure, and specific combinations of bait and lure.

First photo evidence of Siberian Weasel Mustela sibirica Pallas, 1773 (Mammalia: Carnivora: Mustelidae) in Gaurishankar Conservation Area, Nepal

Five photographs of Siberian Weasel were captured by camera traps in two locations at an elevation of 2,840-3,200 m. in Gaurishankar Conservation Area. The species was identified based on its uniform yellowish-brown coat, the presence of a black mask that surrounded its eyes and the white chin, which are key characteristics that distinguishes it from other weasel species. This is the first confirmation of the presence of Siberian Weasel in Gaurishankar Conservation Area, Nepal. Based on present and previous confirmed records, a distribution map of the species has been updated for Nepal.

From past habitats to present threats: tracing North American weasel distributions through a century of climate and land use change

ContextShifts in climate and land use have dramatically reshaped ecosystems, impacting the distribution and status of wildlife populations. For many species, data gaps limit inference regarding population trends and links to environmental change. This deficiency hinders our ability to enact meaningful conservation measures to protect at risk species.ObjectivesWe investigated historical drivers of environmental niche change for three North American weasel species (American ermine, least weasel, and long-tailed weasel) to understand their response to environmental change.MethodsUsing species occurrence records and corresponding environmental data, we developed species-specific environmental niche models for the contiguous United States (1938–2021). We generated annual hindcasted predictions of the species’ environmental niche, assessing changes in distribution, area, and fragmentation in response to environmental change.ResultsWe identified a 54% decline in suitable habitat alongside high levels of fragmentation for least weasels and region-specific trends for American ermine and long-tailed weasels; declines in the West and increased suitability in the East. Climate and land use were important predictors of the environmental niche for all species. Changes in habitat amount and distribution reflected widespread land use changes over the past century while declines in southern and low-elevation areas are consistent with impacts from climatic change.ConclusionsOur models uncovered land use and climatic change as potential historic drivers of population change for North American weasels and provide a basis for management recommendations and targeted survey efforts. We identified potentially at-risk populations and a need for landscape-level planning to support weasel populations amid ongoing environmental changes.

Tracking the decline of weasels in North America.

Small carnivores are of increasing conservation concern globally, including those formerly thought to be widespread and abundant. Three weasel species (Mustela nivalis, M. frenata, and M. erminea) are distributed across most of North America, yet several recent studies have reported difficulty detecting weasels within their historical range and several states have revised the status of weasels to that of species of conservation concern. To investigate the status and trends of weasels across the United States (US) and Canada, we analyzed four separate datasets: historical harvests, museum collections, citizen scientist observations (iNaturalist), and a recent US-wide trail camera survey. We observed 87–94% declines in weasel harvest across North America over the past 60 years. Declining trapper numbers and shifts in trapping practices likely partially explain the decline in harvest. Nonetheless, after accounting for trapper effort and pelt price, we still detected a significant decline in weasel harvest for 15 of 22 evaluated states and provinces. Comparisons of recent and historical museum and observational records suggest relatively consistent distributions for M. erminea, but a current range gap of >1000 km between two distinct populations of M. nivalis. We observed a dramatic drop-off in M. frenata records since 2000 in portions of its central, Great Lakes, and southern distribution, despite extensive sampling effort. In 2019, systematic trail camera surveys at 1509 sites in 50 US states detected weasels at 14 sites, all of which were above 40o latitude. While none of these datasets are individually conclusive, they collectively support the hypothesis that weasel populations have declined in North America and highlight the need for improved methods for detecting and monitoring weasels. By identifying population declines for small carnivores that were formerly abundant across North America, our findings echo recent calls to expand investigations into the conservation need of small carnivores globally.

THE CURRENT SITUATION ANALYSIS AT THE PARASITE FAUNA OF SEMI-AQUATIC CARNIVORES OF THE WEASEL FAMILY IN THE CENTRAL REGION OF THE RUSSIAN FEDERATION

Most members of the Mustelidae family living in the Central Non-Black Earth Region of Russia are the objects of sport and commercial hunting. Some of them are bred in fur farms (mink, polecat) and kept at home as decorative animals. The close contact of a person with various members of the family of mustelids, which increase with the development of urbanization processes, makes significant role of mustelids as sources of dangerous invasions for humans and animals (trichinosis, echinococcosis, etc.). We examined 48 ferrets, 107 American minks, 25 European minks, and 11 otters in order to determine the species composition of animal parasites, in the period 2000–2018. They were examined according to methods commonly used in parasitology about muscle tissue, internal organs, and thoracic and abdominal cavity. Animals for research were obtained from hunters from the Central region of the Russian Federation. Studies have shown that ferrets are invased with 8 species of parasites belonging to two classes: Trematoda (3 species) and Nematoda (5 species). The parasitic fauna of the minks was represented by 15 species of worms: Trematoda (2 species), Cestoda (1 species), Nematoda (12 species). The American mink is infested with 14 helminth species and the European mink with 11 species. Otters were infested with 2 classes of parasites: Trematoda (1 species) and Nematoda (1 species). We explain the high contamination of ferrets and minks of E. perfoliatus by the constant presence of animals at the reservoirs where the intermediate owners of helminths (fish) live. Also, a significant proportion in the diet of many species of weasels are tailless amphibians (frogs), which explains the infection of semi-aquatic animals with an unusual species of trematodes Alaria alata (larvae).

Growth overshoot and seasonal size changes in the skulls of two weasel species.

Ontogenetic changes in mammalian skulls are complex. For a very few species (i.e. some Sorex shrews), these also include seasonally driven, bidirectional size changes within individuals, presumably to reduce energy requirements during low resource availabilities. These patterns are poorly understood, but are likely most pronounced in high-metabolic species with limited means for energy conservation. We used generalized additive models to quantify the effect of location, Julian day, age and sex on the length and depth of 512 and 847 skulls of stoat (Mustela erminea) and weasel (M. nivalis) specimens collected throughout the northern hemisphere. Skull length of both species varies between sexes and geographically, with stoat skull length positively correlated with latitude. Both species demonstrate seasonal and ontogenetic patterns, including a rare, absolute growth overshoot in juvenile braincase depth. Standardized braincase depths of both species peak in their first summer, then decrease in their first winter, followed by a remarkable regrowth that peaks again during their second summer. This seasonal pattern varies in magnitude and timing between geographical regions and the sexes, matching predictions of Dehnel's phenomenon. This suggests implications for the evolution of over-wintering strategies in mammals, justifying further research on their mechanisms and value, with implications for applied osteology research.

Factors Affecting the Distribution of the Japanese WeaselMustela itatsiand the Siberian WeaselM. sibiricain Japan

The vertical distribution of introduced Siberian weasels Mustela sibirica and endemic Japanese weasels M. itatsi in the Seburi Mountains in Kyushu, Japan, was examined from October 1996 to February 1998. Siberian weasels occurred near villages with paddy and cultivated fields, whereas Japanese weasels occurred in grasslands and plantations. The dispersion of yearlings destabilized the distributions of both weasel species. The horizontal distribution of both species throughout Japan was examined by means of collection of dead specimens and by trapping from March 1998 to March 2002. The eastern boundary of the distribution of the Siberian weasel was Fukui, Nagano, and Aichi prefectures; however, the distribution is expanding slowly eastward. The Siberian weasel cannot invade new habitats that lack nearby villages in Seburi, and cannot expand its range in the eastern area of Aichi, where Japanese weasels are dominant. The presence of the Japanese weasel likely prevents expansion of the distribution of the Siberian weasel.

Phylogenetic analysis of mammalian maximal oxygen consumption during exercise

We compiled published values of mammalian maximum oxygen consumption during exercise ( ) and supplemented these data with new measurements of for the largest rodent (capybara), 20 species of smaller-bodied rodents, two species of weasels and one small marsupial. Many of the new data were obtained with running-wheel respirometers instead of the treadmill systems used in most previous measurements of mammalian . We used both conventional and phylogenetically informed allometric regression models to analyze of 77 'species' (including subspecies or separate populations within species) in relation to body size, phylogeny, diet and measurement method. Both body mass and allometrically mass-corrected showed highly significant phylogenetic signals (i.e. related species tended to resemble each other). The Akaike information criterion corrected for sample size was used to compare 27 candidate models predicting (all of which included body mass). In addition to mass, the two best-fitting models (cumulative Akaike weight=0.93) included dummy variables coding for three species previously shown to have high (pronghorn, horse and a bat), and incorporated a transformation of the phylogenetic branch lengths under an Ornstein-Uhlenbeck model of residual variation (thus indicating phylogenetic signal in the residuals). We found no statistical difference between wheel- and treadmill-elicited values, and diet had no predictive ability for . Averaged across all models, the allometric scaling exponent was 0.839, with 95% confidence limits of 0.795 and 0.883, which does not provide support for a scaling exponent of 0.67, 0.75 or unity.

The natural history of weasels and stoats: ecology, behavior, and management

1. Weaselly distinguished, stoatally different 2. Hair trigger mouse traps with teeth 3. Molt and winter whitening 4. Body size 5. Food 6. Hunting behavior 7. The impact of predation by weasels on populations of natural prey 8. Adjustable living spaces 9. Reproduction 10. Populations: density and breeding success 11. Populations: survival and mortality 12. Human attitudes to weasels in their native environments 13. Stoats as introduced pests in New Zealand 14. Puzzles: sexual dimorphism, delayed implantation and co-existence among weasel species Conclusion

The impact of short‐term predator removal on vole dynamics in an arctic‐alpine landscape

During 1991–95, mammalian predators (weasel, Mustela nivalis, stoat, M. erminea, mink, M. vison, and red fox, Vulpes vulpes) were excluded in late summers from a 2 ha piece of a north Norwegian mountain slope. The exclosure extended from an outpost of luxuriant sub‐arctic birch forest to a typical arctic–alpine habitat complex, including productive willow scrublands, tundra heaths, dry ridges and snow‐beds. The exclosure thus encompassed the entire range of habitat conditions encountered in a typical north Fennoscandian mountain and tundra landscapes. During 1991–95, the exclosure was predator‐proof from late July to late September. In wintertime and in early summer, the exclosure was accessible to mammalian predators. Vole dynamics in the short‐term exclosure were compared to dynamics in five reference areas with similar habitat conditions.In 1991, when vole densities were rising in the area, neither collective vole densities nor densities of individual vole species differed significantly between the exclosure and the replicated controls. Spring densities of voles were never significantly different between the exclosure and the controls. With respect to autumnal densities of voles, however, the exclosure was a statistical outlier in the peak year 1992 and throughout the gradual decline phase of 1993–95. In the peak year, the difference in collective vole densities was modest (30%), but increased to two‐fold during the first two decline years and was almost four‐fold in the crash year of 1995. The strongest response was displayed by field voles (Microtus agrestis), hypothesized to be the pivotal prey species of weasels, especially by females and young individuals, i.e. by the functional categories especially sensitive to mammalian predation. These results are consistent with the hypothesis that predation plays a pivotal role for the regulation of herbivorous mammals in relatively productive arctic–alpine habitats.

Variation in body size, sexual dimorphism and age-specific survival in stoats,Mustela erminea(Mammalia: Carnivora), with fluctuating food supplies

Most hypotheses attempting to explain the evolution of pronounced sexual dimorphism in body size in the three species of weasels (Mustela erminea,M. frenata,M. nivalis) assume that sexual dimorphism is a long-term adaptation, associated with the different reproductive strategies of the two sexes. We here examine an auxiliary hypothesis which predicts that the degree of sexual dimorphism may also vary over the short-term, because when food is temporarily abundant, sexual selection should favour a greater growth rate of males than of females. This hypothesis concerns a phenotypic response which could introduce temporarily increased variation into an existing genotypic trait. We document the present size and sexual dimorphism of stoats introduced last century to New Zealand from Britain in relation to between-year variation in food supply in a single habitat (forests of southern beech,Nothofagussp.). Southern beech trees produce heavy crops of flowers and seed at 3–5 year intervals, which are associated with very variable supplies of important prey of stoats, including several species of seed-eating birds, litter-feeding insects, and feral house mice (Mus musculus). Alternative prey are scarce. Regressions of condylobasal length and head-body length on mouse population indices were significant in both sexes. Mean condylobasal length was larger in both male and female stoats born after a heavy seedfall compared with those born in non-seedfall years. However, the largest males born in years of heavy seedfall were removed by selective mortality before the age of 3 years, so the condylobasal lengths for old (≥3.0 yr) males converged on a common mean regardless of food supply in their birth year. Sexual dimorphism did not vary with food supplies (as reflected in seedfall records or mouse population indices) at any age. First-year survivorship, at least from the age of independence, was significantly negatively correlated with density of stoats in the summer of their birth year.

Variation in body size, sexual dimorphism and age-specific survival in stoats, Mustela erminea (Mammalia: Carnivora), with fluctuating food supplies

Most hypotheses attempting to explain the evolution of pronounced sexual dimorphism in body size in the three species of weasels (Mustela erminea,M. frenata,M. nivalis) assume that sexual dimorphism is a long-term adaptation, associated with the different reproductive strategies of the two sexes. We here examine an auxiliary hypothesis which predicts that the degree of sexual dimorphism may also vary over the short-term, because when food is temporarily abundant, sexual selection should favour a greater growth rate of males than of females. This hypothesis concerns a phenotypic response which could introduce temporarily increased variation into an existing genotypic trait. We document the present size and sexual dimorphism of stoats introduced last century to New Zealand from Britain in relation to between-year variation in food supply in a single habitat (forests of southern beech,Nothofagussp.). Southern beech trees produce heavy crops of flowers and seed at 3–5 year intervals, which are associated with very variable supplies of important prey of stoats, including several species of seed-eating birds, litter-feeding insects, and feral house mice (Mus musculus). Alternative prey are scarce. Regressions of condylobasal length and head-body length on mouse population indices were significant in both sexes. Mean condylobasal length was larger in both male and female stoats born after a heavy seedfall compared with those born in non-seedfall years. However, the largest males born in years of heavy seedfall were removed by selective mortality before the age of 3 years, so the condylobasal lengths for old (≥3.0 yr) males converged on a common mean regardless of food supply in their birth year. Sexual dimorphism did not vary with food supplies (as reflected in seedfall records or mouse population indices) at any age. First-year survivorship, at least from the age of independence, was significantly negatively correlated with density of stoats in the summer of their birth year.

Inter‐ and Intraspecific Character Displacement in Mustelids

In a search for possible community—wide character displacement (manifested as equal size ratios between adjacent morphospecies in a size—ranking), we examined the weasels (Mustela) of North America and also the mustelid—viverrid guild of Israel. We measured condylobasal skull length (CBL) and maximal diameter of the upper canine (Csup L) on museum specimens of the two or three weasel species sympatric at each of eight North American sites. We found substantial geographic variation and, at each site, pronounced sexual dimorphism of each species, as well as geographic variation in the degree of sexual dimorphism. With conspecific males and females viewed as separate "morphospecies," we found little variance about the mean measurement for a morpho—species at each site, and almost no overlap of distributions between sympatric morpholo—species. In site of the geographic variation, at seven of the eight sites the size ratios for CsupL between adjacent morphospecies in a size—ranking were remarkably equal, while the analogous analysis for CBL showed ratios tending towards equality at only four sites. Indications of equal ratios were largely absent for both variables when sexes were analyzed separately. For a more taxonomically diverse "mustelid—viverrid" guild of five species in Israel, the 10 ranked morphospecies had extraordinarily equal size ratios for CsupL but not for CBL, a result maintained if sexes were analyzed separately. These results, plus information on feeding behavior of mustelids, seem consistent with a hypothesis of competitive character displacement, but many critical data remain uncollected. There is no direct evidence that prey are limiting to either guild, data are scant on what the morphospecies actually eat, and there is no functional analysis for these species of the role of canine or skull size in ability to kill prey of different sizes and types. Sexual selection based on canine display or fighting might well contribute to sexual dimorphism. Though direct observation is lacking, it is also possible that canines may be used in threats or fighting in interspecific encounters. However,it seems unlikely that such canine use could account for the entire pattern of size ratio equality, as it would be quite coincidental that size ratios sexually selected between sexes within species should happen to equal those, however selected, between the male of each species and the female of the next larger species.

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

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 Subspecies Category in Mammals

N THE early part of the present century collections of mammals were from widely scattered localities throughout North America, and nothing was known about the vast intervening areas. It was natural, therefore, to assign full specific rank to nearly every kind of mammal that was dignified with a latinized name. As collections increased, and as geographic gaps narrowed, it became apparent that some of the species had more or less unbroken ranges that extended to those of other named kinds. As a consequence, the number of species decreased and the number of subspecies increased. At the time of Osgood's revision of the genus Peromyscus (1909) most of the named kinds of North American mammals were given full specific rank. Accordingly, there were some 28 species of Peromyscus that were destined to become subspecies or synonyms of what Osgood considered to be one species, maniculatus. Thus, it was Osgood's classical work that focused thinking in terms of the trinomial rather than the binomial, as had been common practice among his predecessors as well as many of his contemporaries. To cite two more examples, Miller listed 24 species of weasels (Mustela) in his 1911 checklist (1912) and 25 species in his 1923 checklist (1924); Hall (1951) reduced the number of species of weasels occurring over the same geographic area to three, with 60 subspecies. In the coyotes of the genus Canis, Miller (op. cit.) listed 14 species; these were recently grouped under one species by Jackson (1951), with 19 subspecies. This does not indicate that evolution has been going on in reverse. It does indicate that our interpretations now are quite different from those of students of 50 years ago. Along with the change in evaluation of the lower categories, there grew up a school, of which I was one, of subspecies describers. I fear that the objective of many in this group was to discern small differences in samples of populations from different localities rather than to study the similarities of the samples, or the variability within a population. Our most horrible example of what can result from this indiscriminate naming of local populations is to be seen in the present literature on pocket gophers of the genus Thomomys. In one species, T. bottae, we now have listed more than 150 subspecies, and there are more to come. If this continues, eventually every colony of Thomomys bottae will bear a formal name recognized by the International Commission on Zoological Nomenclature. It is now necessary to have a large-scale map just to indicate the type localities of all the subspecies of Thomomys bottae. What does all this show from the biological point of view? It shows that Thomomys bottae is highly variable throughout its range. But is it necessary to have 150 or more names in the literature to show this? I think not. I sincerely believe that the variations in most of the morphological characters used as bases for naming the subspecies could be shown with symbols on a map, as some of the botanists have been doing with plants and as Blair (1953) attempted to do with Peromyscus. Blair's symbols