The diet of the feral mink (Mustela vison) in southwest Britain

Mink diet in three study areas in southwest Britain was studied by faeces (scat) analysis. In these areas mink ate a wide range of prey, mainly fish, birds and mammals. Proportions of prey in the diet were determined largely by availability, but were also affected by prey behaviour, the physical nature of the habitat and overall prey abundance. Seasonal variation in predation was recorded on moorhens and fish. Changes in rod and net fishing success on the river Teign could not be correlated with the arrival of the mink. Changes in fish populations in Slapton Ley appeared to have causes other than mink. It is concluded that, in the areas studied, domestic stock make up a very small proportion of the mink's diet, and that the wild prey species are not suffering any obvious population depletion.     

The impact of the American mink (Neovison vison) on native vertebrates in mountainous streams in Central Spain

The American mink (Neovison vison) is responsible for the widespread decline of its prey species in the regions where it is an invasive species. The current expansion of the mink in the Iberian Peninsula has aroused concern among conservationists about its negative impact on the rich native fauna. However, evidence for this is still scarce, although there are several studies establishing a direct causal relationship between declining native species and the presence of the American mink. Thus, it is important to further investigate the responses of native species to the American mink in several habitats and locations to enhance our knowledge about the patterns of the effect of the mink in Spain, as well as to inform conservation actions. A field study of the impact of the American mink on a mountainous vertebrate community in central Spain is presented. We studied six species: two fish, one amphibian, one bird, and two mammals. The general results showed a species-specific sensitivity to mink presence, with the Mediterranean water shrew (Neomys anomalus) and the southern water vole (Arvicola sapidus) being the most affected because their ranges were significantly decreased after the introduction of the mink. Regarding the other species, neither their abundance nor range was apparently affected by the American mink. The predatory behavior of the mink and interactions with other carnivores could account for these results. These data aid in shedding light about the current impact of the mink on invaded areas of the Iberian Peninsula and highlight the variability of its effects, as well as the urgent need to establish a general program of control of the mink to avoid negative effects upon native prey communities. Furthermore, given the different responses of native species, we propose that measures to protect native species should be based on species-specific goals and attributes.     

Decline of invasive alien mink (Mustela vison) is concurrent with recovery of native otters (Lutra lutra)

Invasive species often cause the decline of native prey or competitors. We highlight a contrasting example of the large-scale recovery of a native species and the concurrent decline and likely displacement of an established invasive competitor. Invasive American mink Mustela vison became widespread in the British Isles at the same time as native Eurasian otters Lutra lutra were declining as a result of water pollution. In common with other invasive predators, mink cause conservation problems for a range of native prey species, most notably water voles Arvicola terrestris . Recent trends in the distribution of native otters and invasive mink in north-east England were examined using a novel regression modelling approach to analyse presence/absence data from field surveys, corroborated by contemporary predator culling records. Between 1991 and 2002, the percentage of sites where mink signs were found decreased from 80% to 20%, while otter signs increased from 18% to 80%. Annual indices of mink captures on shooting estates increased between 1980 and 1996, but were followed by a decline thereafter. Indices of the incidence of native otters were significantly related to those indicating the decline or displacement of invasive mink. This large-scale field study is supportive of localized experimental evidence for the return of dominant, native otters being concurrent with the decline of the invasive alien mink. The recovery of a dominant native species may represent a reversal of the mesopredator release that allowed invasive mink to establish and may eventually serve to mitigate their impact on native prey species.     

Food niche variation of European and American mink during the American mink invasion in north-eastern Belarus

Understanding processes allowing the co-existence of ecologically similar species is important but difficult to study in community ecology. Introductions of alien species are unplanned experiments allowing investigation of co-adaptation of both native and invasive species over a short period. We analysed food niche differentiation between native European mink and alien American mink after invasion of the latter species in Belarus. European mink feed mainly on crayfish, frogs and fish whereas American mink prefer small mammals, fish and frogs. The diet of both species varied between seasons and during the period of alien mink invasion. Concurrent with the progress of American mink invasion, the European mink food niche has narrowed to feeding mainly on frogs, with the proportion of aquatic prey (fish and crayfish) in their diet drastically reduced. In contrast, the American mink food niche became wider during invasion. The breadth was stable but included a varied proportion of different prey categories: namely an increased proportion of aquatic prey and a decreased proportion of water vole and waterfowl. The increase in abundance of American mink saw a decrease in the proportion of larger prey in their diet. When American mink preyed more often on frogs, food niche overlap of both predators increased. This result suggests that arrival of an alien competitor reduced food abundance (exploitative competition) and caused a change in native mink diet.     

Prey preference of large carnivores in Anamalai Tiger Reserve,India

Prey preferences of large carnivores (tiger (Panthera tigris), leopard (Panthera pardus) and dhole (Cuon alpinus)) in the tropical forest of Anamalai Tiger Reserve (ATR) were evaluated. This was the first study in ATR to estimate the density of prey and the food habits of these large carnivores. The 958-km² intensive study area was found to have a high mammalian prey density (72.1 animals per square kilometre) with wild boar (20.61 animals per square kilometre) and chital (20.54 animals per square kilometre) being the most common species, followed by nilgiri tahr (13.6 animals per square kilometre). When the density figures were multiplied by the average weight of each prey species, a high biomass density of 14,204 kg km⁻² was obtained for the intensive study area. Scat analysis and incidental kill observation were used to determine the dietary composition of these predators. During the study from the period of March 2001 to April 2004, 1,145 tiger scats, 595 leopard scats and 2,074 dhole scats were collected and analysed. Kill data were based on direct observation of 66 tiger kills and 39 leopard kills. Sambar, with a density of 6.54 kg km⁻² was the preferred prey for these carnivores. Sambar constitutes 35% of the overall diet of tiger, whereas it constitutes 17% and 25% in leopard and dhole diets, respectively. Chital was utilized less than sambar in the range of about 7%, 11% and 15% by tiger, leopard and dhole, respectively. Predator diet was estimated more accurately by scat analysis, which reveals 30% of smaller prey species in leopard’s diet, which was not observed by kill data. This study reveals that ATR harbours high prey density, and these large carnivores seem mostly dependent on the wild prey rather than on domestic livestock as in some other areas in the subcontinent. These factors make ATR a potential area for long-term conservation of these endangered carnivores.     

The diet of an invasive nonnative predator,the feral ferret <Emphasis Type="Italic">Mustela furo</Emphasis>, and implications for the conservation of ground-nesting birds

Introduced carnivores have had a significant impact on the fauna of a number of countries, particularly on islands. In the British Isles, several offshore islands holding internationally important aggregations of seabirds and shorebirds support self-sustaining feral ferret Mustela furo populations, often as the top terrestrial predator. However, little is known about the interactions between ferrets and both native and nonnative prey in these locations. We examined the diet of feral ferrets on Rathlin Island, Northern Ireland. We determined the frequency of occurrence of prey items and constructed energetic models to determine their potential impact on both native and introduced prey. Rabbits Oryctolagus cuniculus occurred in 75% of scats, while birds, carrion, and brown rats Rattus norvegicus were important secondary items. There was little difference between the diets of males and females. Estimates of the energy requirements of the population at current, and with hypothetically reduced, rabbit availability revealed the potential for carrion to maintain the ferret population over winter. Management options could thus focus on reducing anthropogenic food sources as an immediate way of mitigating the threat to ground-nesting birds, while other strategies, including eradication, are considered.     

Assessing the cryptic invasion of a domestic conspecific: American mink in their native range

Control of invasions is facilitated by their early detection, but this may be difficult when invasions are cryptic due to similarity between invaders and native species. Domesticated conspecifics offer an interesting example of cryptic invasions because they have the ability to hybridize with their native counterparts, and can thus facilitate the introgression of maladaptive genes. We assessed the cryptic invasion of escaped domestic American mink (Neovison vison) within their native range. Feral mink are a known alien invader in many parts of the world, but invasion of their native range is not well understood. We genetically profiled 233 captive domestic mink from different farms in Ontario, Canada and 299 free‐ranging mink from Ontario, and used assignments tests to ascertain genetic ancestries of free‐ranging animals. We found that 18% of free‐ranging mink were either escaped domestic animals or hybrids, and a tree regression showed that these domestic genotypes were most likely to occur south of a latitude of 43.13°N, within the distribution of mink farms in Ontario. Thus, domestic mink appear not to have established populations in Ontario in locations without fur farms. We suspect that maladaptation of domestic mink and outbreeding depression of hybrid and introgressed mink have limited their spread. Mink farm density and proximity to mink farms were not important predictors of domestic genotypes but rather, certain mink farms appeared to be important sources of escaped domestic animals. Our results show that not all mink farms are equal with respect to biosecurity, and thus that the spread of domestic genotypes can be mitigated by improved biosecurity.     

Facultative predation and scavenging by mammalian carnivores: seasonal,regional and intra‐guild comparisons

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Surplus killing by carnivores

In several field observations, foxes, Spotted hyaenas and other carnivores killed many more prey individuals than they could eat. Functional and causal aspects of this phenomenon are discussed and the conclusion is reached that these surplus kills are the consequence of behavioural compromises in both predator and prey to meet opposing environmental requirements.  

Summary:

(1) Observations are reported in which carnivores killed considerably more prey animals than they could possibly eat, and causal and functional aspects of this behaviour are discussed. The species concerned were especially foxes and Spotted hyaenas, and references are quoted about surplus killing by other Canidae, Felidae and Ursidae.
(2) It is argued that satiation in carnivores does not inhibit further catching and killing , but it probably does inhibit searching and hunting. Thus carnivores are able to procure an "easy prey" but normally satiation limits numbers killed.
(3) Many, if not all, carnivores possess behaviour patterns which allow utilization of a kill at a later time, or allow other members of the same social unit or offspring to use the food.
(4) Several prey species showed a lack of anti-predator reaction under particular climatological circumstances; it is argued that this lack of response usually has survival value. Sometimes anti-predator behaviour is accidentally made ineffective.
(5) Surplus kills are made possible by (2) and (4) above, and only very rare circumstances give a predator access to so many prey that (3) is ineffective. It is suggested that surplus kills are the consequence of behavioural compromises in both predator and prey to meet opposing environmental requirements.     

Aleutian mink disease parvovirus in wild riparian carnivores in Spain

Serious declines in populations of native European mink (Mustela lutreola) have occurred in Europe. One responsible factor may be infectious diseases introduced by exotic American mink (Mustela vison). In order to investigate a possible role for Aleutian mink disease parvovirus (ADV), we surveyed native riparian carnivores and feral American mink. When serum samples from 12 free-ranging European and 16 feral American mink were tested, antibodies to ADV were detected from three of nine European mink. ADV DNA was detected by polymerase chain reaction in whole cell DNA from four of seven carcasses; two American mink, one European mink and a Eurasian otter (Lutra lutra). Lesions typical of Aleutian disease were present in one of the American mink. A portion of the ADV VP2 capsid gene was sequenced and the results suggested that two sequence types of ADV were circulating in Spain, and that the Spanish ADVs differed from other described isolates from North America and Europe. Future conservation and restoration efforts should include measures to avoid introduction or spread of ADV infection to native animals.     

Interactions of exotic and native carnivores in an ecotone, the coast of the Beagle Channel, Argentina

In coasts bordering highly productive seas, there can be a flux of resources to the terrestrial ecosystem, and terrestrial carnivores can use marine prey extensively. Two native, endangered species (otter Lontra provocax and culpeo fox Pseudalopex culpaeus lycoides) and two exotic species (mink Neovison vison and grey fox Pseudalopex griseus) inhabit the Beagle coast. The objectives of this paper are: (1) to describe the diet, habitat use and distribution of otters, mink and foxes on the coast of the Beagle channel and (2) to discuss the role of marine resources in the ecological interactions among these species. Diet was determined from the analysis of 245 faeces, and distribution was established from sign surveys. Marine prey occurred in the scats of 98.3, 70.4, 35.5 and 18.2% of otters, mink, culpeo and grey foxes, respectively. Other terrestrial species also use marine resources in Southern Patagonia. All this evidence suggests that the Fueguian coastal channels provide an illuminating example of allochthonous food subsidies from the sea. In the community of four sympatric predators, two native (and endangered) and two exotic, coexistence appears to be facilitated by a renewing marine food subsidy.     

Underwater predatory behaviour of the American mink (Mustela vison)

Fishing behaviour of the American mink ( Mustela vison Schreber) was investigated in the laboratory. Data were recorded using ciné film and tape recorded commentaries. Three species of prey were presented to mink, namely, carp ( Cyprinus curpio ), goldfish ( Carassius auratus ) and minnows ( Phoxinus phoxinus ).
It was found to be necessary to train ranch-bred mink to enter water and catch fish; young mink appeared to be easier to train than adults. Mink spent 5–20 sec under water when fishing; prey had usually previously been located from an aerial vantage point. Predatory behaviour was highly organized sequentially whereas fish were more prone to indulge in unpredictable stratagems; the behaviour of mink and fish were highly correlated.
The mink's efficiency in catching fish was related to prey size (smaller individuals being more vulnerable to capture) and shoaling. Minnows, which form highly organized shoals, were less easily caught when present in large numbers; this was not true of a loosely shoaling species, the carp.
Of the three species of prey presented, vulnerability to capture took the form goldfish> carp> minnow; these differences, however, may have been influenced by the fish's previous experience of underwater predators.     

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.     

Restoration programmes and the development of a natural diet: a case study of captive-bred European mink

As part of a conservation initiative, we released captive-bred individuals of European mink (Mustela lutreola) onto a Baltic island ‘sanctuary’, Hiiumaa (Estonia), and investigated the development of their diet in the wild. Fifty-four animals out of the 172 released were equipped with radio collars and tracked in 2000–2003 intensively after release. Based on the analysis of the contents of 564 collected scats, we monitored how the diet of released individuals changed after release and how this was affected by habitat and by season. Diet changed as they adapted to the wild: some prey consumed immediately after release were later substituted with prey more typical of wild European mink elsewhere. The mink’s tendency to take typical prey increased (crayfish, 3; fish, 1.5; and small mammals, 2 times), while the proportion of atypical prey decreased more than five times in 60 days after release. Once established in the wild, the composition of the diet and its variation between seasons, habitats or weather conditions were similar to that reported elsewhere for wild European mink. There is no indication therefore that the components of the diet provided in captivity persisted in the wild after the adaptation period. We suggest that the adaptation of released carnivores to natural prey merits more attention in reintroduction projects.     

The role of exotic mammals in the diet of native carnivores from South America

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Feeding habits of three sympatric mammals in NE Spain: the American mink, the spotted genet, and the Eurasian otter

Diet composition, niche measures, and prey consumption of three sympatric species of carnivores, one non-native and introduced, the American minkNeovison vison Schreber, 1777, and two native, the spotted genetGenetta genetta Linnaeus, 1758 and the Eurasian otterLutra lutra Linnaeus, 1758, were studied in a Spanish Mediterranean area. The study was based on the analysis of prey remains in the faeces of the predators. Faeces of mink (n = 444), genet (n = 310), and otter (n = 108) were collected all year round for four years along the Llobregat (21 km) and Gavarresa rivers (12 km). Simultaneously, and in the same area, prey species density and weight were estimated by means of trapping. The diet of mink and genet was dominated by the American crayfishProcambarus clarkii, while the otter fed almost exclusively on fish. Compared to the mink, the genet seemed to specialise more on small mammals while the mink specialised more on aquatic birds, especially in autumn-winter. Niche overlap was higher between mink and genet than between either of them and the otter.     

Dogs Canis familiaris as carnivores: their role and function in intraguild competition

• 1 Dogs Canis familiaris are the world's most common carnivore and are known to interact with wildlife as predators, prey, competitors, and disease reservoirs or vectors.
• 2 Despite these varied roles in the community, the interaction of dogs with sympatric wild carnivore species is poorly understood. We review how dogs have been classified in the literature, and illustrate how the location and ranging behaviour of dogs are important factors in predicting their interactions with wild prey and carnivores.
• 3 We detail evidence of dogs as intraguild competitors with sympatric carnivores in the context of exploitative, interference and apparent competition.
• 4 Dogs can have localized impacts on prey populations, but in general they are not exploitative competitors with carnivores. Rather, most dog populations are highly dependent on human‐derived food and gain a relatively small proportion of their diet from wild prey. However, because of human‐derived food subsidies, dogs can occur at high population densities and thus could potentially outcompete native carnivores, especially when prey is limited.
• 5 Dogs can be effective interference competitors, especially with medium‐sized and small carnivores. Dogs may fill the role of an interactive medium‐sized canid within the carnivore community, especially in areas where the native large carnivore community is depauperate.
• 6 Dogs can also be reservoirs of pathogens, because most populations around the world are free‐ranging and unvaccinated. Diseases such as rabies and canine distemper have resulted in severe population declines in several endangered carnivores coexisting with high‐density dog populations. Dogs can therefore be viewed as pathogen‐mediated apparent competitors, capable of facilitating large‐scale population declines in carnivores.
• 7 Based on this information, we propose conceptual models that use dog population size and ranging patterns to predict the potential for dogs to be intraguild competitors. We discuss how interactions between dogs and carnivores might influence native carnivore communities.

     

Differences in diet and trophic interactions of Patagonian carnivores between areas with mostly native or exotic prey

The prey base for Patagonian carnivores has been altered greatly over the past 150 years due to widespread overgrazing by livestock, invasions by exotic wildlife, and hunting. On ranches in northern Patagonia carnivores consume mostly exotic species, and native herbivores are ecologically extinct in their role as prey. In this study we compare diets of the culpeo (Lycalopex culpaeus), chilla (L. griseus), puma (Puma concolor), Geoffroy's cat (Leopardus geoffroyi), colocolo (L. colocolo), and hog-nosed skunks (Conepatus chinga and C. humboldtii) in a reserve with a mostly native prey base to their diets on the ranches, and evaluate how differences in prey bases affect trophic interactions among carnivores. Carnivores in the reserve consumed mostly native prey. Dietary overlap among carnivores was not significant on the reserve, but was highly significant on the ranches. This homogenization of diets where densities of native species are reduced could lead to stronger negative interactions among carnivores, altering the composition of the carnivore assemblage to the detriment of the more specialized species. Study of carnivore diets may be a relatively quick way to evaluate the conservation status and ecological functionality of prey assemblages in Patagonia and other areas where these have been altered.     

Short-term fasting induces intra-hepatic lipid accumulation and decreases intestinal mass without reduced brush-border enzyme activity in mink (<Emphasis Type="Italic">Mustela vison</Emphasis>) small intestine

For many mammalian species short-term fasting is associated with intestinal atrophy and decreased digestive capacity. Under natural conditions, strictly carnivorous animals often experience prey scarcity during winter, and they may therefore be particularly well adapted to short-term food deprivation. To examine how the carnivorous gastrointestinal tract is affected by fasting, small-intestinal structure, brush-border enzyme activities and hepatic structure and function were examined in fed mink (controls) and mink that had been fasted for 1–10 days. During the first 1–2 days of fasting, intestinal mass decreased more rapidly than total body mass and villus heights were reduced 25–40%. In contrast, tissue-specific activity of the brush-border enzymes sucrase, maltase, lactase, aminopeptidase A and dipeptidylpeptidase IV increased 0.5- to1.5-fold at this time, but returned to prefasting levels after 6 days of fasting. After 6–10 days of fasting there was a marked increase in the activity of hepatic enzymes and accumulation of intra-hepatic lipid vacuoles. Thus, mink may be a useful model for studying fasting-induced intestinal atrophy and adaptation as well as mechanisms involved in accumulation of intra-hepatic lipids following food deprivation in strictly carnivorous domestic mammals, such as cats and ferrets.Communicated by I.D. Hume     

Trophic ecology of a top predator colonizing the southern extreme of South America: Feeding habits of invasive American mink (Neovison vison) in Tierra del Fuego

The American mink (Neovison vison) is a semi-aquatic, generalist carnivore released onto Tierra del Fuego (TDF) Island in the 1940s, subsequently spreading to adjacent islands in the archipelago with potential effects on native prey populations. Knowledge of this new predator's trophic ecology is essential to identify threats, plan control strategies and conserve native fauna. We studied seasonal mink diet in TDF in different habitats. We identified undigested remains from 493 scats collected between May 2005 and March 2009 along marine coasts and freshwater shores (rivers and lakes). Small mammals and fish were the main mink prey in TDF (over 65% of diet items). Seasonal variations were not detected, but diet did vary significantly between marine and freshwater habitats, where more terrestrial items were consumed. Among mammals, mink consumed more small native rodents than exotic species. Native fish consumption was also important with greater representation of species from the families Nototheniidae and Galaxiidae in marine and freshwater habitats respectively. Birds were the third item in importance, but did not constitute a particularly large part of the mink's diet on TDF. Overall, differences found in mink diet between habitats reflected their generalist/opportunistic feeding behaviour and did not differ greatly from observations in its native range or in other areas where it has been introduced. Our results establish the interactions between this novel predator and its prey and also illustrate the need to continue research on native prey populations to quantify mink impact on them and understand the ecological context of this biotic assemblage.