Early research on farmed mink was predominantly concerned with increased productivity; however, in recent years there have been an increasing number of studies related to welfare. The biology of feral mink has also become better understood, and such knowledge can aid in the assessment of welfare on farms, or in the interpretation of problems related to captivity. This paper is a comprehensive review of research pertinent to the welfare of farmed American mink, Mustela vison, in relation to their housing and management. It indicates how housing conditions might be changed to improve welfare, and where our present knowledge is insufficient. Many significant aspects of mink behaviour in the wild, such as their lack of social contact, their tendency to travel long distances and use several den sites, and regular swimming and diving, are denied them in captivity. Farmed mink also show high levels of stereotypy, suggesting that their welfare is not good. Welfare may be improved by appropriate environmental enrichment and changes in the social environment of farmed mink. In general, studies aimed at improving housing conditions have been limited in scope and outlook.

The effects of cage enrichments and additional space were studied in 60 pairs of mink kits kept in standard cages (STD) and 67 pairs of mink kits kept in enriched cages (ENR). During the period from mid July to the end of September both groups had alternate access to one and two connected cages. From October, half of the mink in each group had permanent access to one cage and the other half permanent access to two cages. The enrichment of the cages consisted of extra resting places (tubes made of wire mesh and plastic) and occupational materials in terms of table-tennis balls and ropes to pull and chew. The mink were observed for an experimental period of nine months, from late lactation until the beginning of the following mating season. The welfare was assessed through behavioural traits (use of nest box and enrichments, activity out in the cage, stereotypies and fur-chewing) consumption of food and straw, bodyweight and level of faecal corticoid metabolites. The presence of enrichments resulted in less tail-chewing, fewer stereotypies, and a reduced level of faecal corticoid metabolites. In addition, the presence of enrichments led to fewer social interactions and reduced the consumption of straw. Regarding the frequency of utilising different occupational materials, the mink did not use the table-tennis balls, but the tubes and pull-ropes were given extensive use. Access to one or double cages had no effect on stereotypies, fur-chewing and physiology linked to welfare, but mink with access to double cages used the nest box less, had a lower consumption of straw and pull-ropes than the mink with access to only one cage. However, there were no indications of frustration when the mink were deprived of using double cages. We conclude that increased environmental complexity in the form of occupational materials improved the welfare of the mink, whereas doubling the cage size had little or no effect in relation to mink welfare.

The American mink Mustela vison has spread widely beyond its native North American range and is associated with problems for the conservation of native species because of its impact as both predator and competitor. We investigated the impact of feral mink on waterfowl in Lanín National Park, south-west Neuquén, Patagonia, Argentina, an area in which the predator is currently expanding. Statistically significant differences were observed in the number of waterfowl species at lakes without mink (7.3 ± SE 0.7) compared to those with mink (4.0 ± SE 0.6). Overall abundance of birds observed per day was higher at lakes without (104.2 ± SE 20.6) than with mink (21.2 ± SE 22.3). The great grebe Podiceps major, speckled teal Anas flavirostris, Chiloe wigeon Anas sibilatrix and red-gartered coot Fulica armillata were more abundant on water bodies without mink, and flocks of the ashy-headed goose Chloephaga poliocephala were larger in areas without mink. Other species, such as the white-tufted grebe Rollandia rolland, coscoroba swan Coscoroba coscoroba, black-necked swan Cygnus melanocoryphus, cinnamon teal Anas cyanoptera, Andean duck Oxyura jamaicensis and Andean gull Larus serranus were never observed in areas harbouring mink. We conclude that at least 12 of the 25 waterfowl species observed are sensitive to the presence of the mink, either being absent or having a lower abundance where mink are present.

The impact of alien American mink on the native fauna of oceanic islands has been demonstrated in a number of locations. In the sub-Antarctic Cape Horn Biosphere Reserve of southern Chile the species is currently expanding in an area where the native fauna evolved in the absence of terrestrial predators. To evaluate any emerging problems we therefore investigated seasonal variation in prey use by mink on Navarino Island within the Reserve. We identified undigested remains in 414 scats collected from the shores of 27 ponds over January–November 2006. Diet consisted mainly of mammals and birds. Mammals, including both native and exotic rodents, were the predominant prey in all seasons but birds were of equal importance during the summer (when birds breed and their abundance and diversity increases on the island). Exotic rodents were the only identifiable mammalian prey item during winter. Native wetland birds constituted a substantial proportion of mink diet, and greater than that reported in other areas. Many birds breeding on Navarino Island are ground-nesting, a strategy that evolved in the absence of native mammalian predators. Considering the international importance of this region, our results emphasize the need for an assessment of the impact of mink predation on the populations of native prey.

There is a considerable amount of literature on the diet and effect of feral American mink Mustela vison on the distribution and abundance of water voles Arvicola terrestris in Britain. Few recent studies, however, have attempted to examine the occurrence of water voles in the diets of native predators. Fox Vulpes vulpes scat and grey heron Ardea cinerea pellets were collected during winter 2003–2004 at a location known to contain a large number of water voles. These scats and pellets were subsequently analysed to determine the frequency of water vole occurrence in the diet of these opportunistic predators. Water vole remains were found in 30% of fox scats analysed and accounted for 13% of the total weight of scats. A total of 18% of heron pellets contained the fur of water voles in addition to the fur of four other rodent species. The potential role of native predators in the loss and fragmentation of site-specific populations of water voles in Britain is further discussed.

Recent advances in molecular scatology have allowed the development of reliable and non-invasive methods that can be applied in monitoring of small carnivores, without disturbance of the animals. Here a method is described that can be used to differentiate European mink Mustela lutreola, polecat M. putorius and American mink M. vison based on the analysis of DNA extracted from faeces. It consists of a nested PCR of a region of the mitochondrial D-loop followed by digestion of the resulting 240 bp amplicons with the restriction enzymes RsaI and MspI. The restriction patterns of both enzymes, when used together, are found to detect species-specific sequence variation. Two different haplotypes for European mink (AA, AB), another two for the polecat (AC, AD) and one for American mink (BC) can also be discriminated by this technique. Two new haplotypes for the mitocondrial D-loop of mustelids are described after DNA sequencing.

American mink Mustela vison are an invasive species in many parts of the world (e.g. Europe, Iceland and South America) and in many of these areas they are a threat to the native wildlife. It is therefore important to establish a reliable and efficient method to estimate their relative abundance in order to manage their populations. In this study, the use of surveys of signs (scats and footprints) as a way to estimate the relative abundance of American mink was evaluated. Populations of mink in three areas of England were studied to evaluate the impact of three factors (surveyor, marking places and month) on the probability of deposition and detection of signs. Among these factors only month had a significant effect. In the second part of the study, sign surveys were compared with live trapping and it was found that the proportion of sections with mink signs was only loosely correlated to the abundance of mink as estimated from live trapping. In conclusion, this study suggests that, provided that surveyors are trained, that there is a sufficient number of marking places in each section, and that the surveys are carried out in comparable seasons, sign surveys are an appropriate way to monitor the relative abundance of mink. Sign surveys are better than trapping when it is necessary to monitor mink populations over large areas because they are less time consuming, require less manpower and are cheaper.

Endangered southern river otters Lontra provocax (huillin) are confined to southern Chile and three isolated areas of Argentina, the most important being the Nahuel Huapi National Park, where distribution surveys were conducted in 1983, 1995 and 2000. We used these survey data together with a Geographical Information System analysis to elucidate the factors that are important in determining huillin distribution at different ecological scales. There were significant heterogeneities in the distribution of huillin between river basins, between habitats, between lakes relative to dispersal routes and topography, and between sample points within a lake. From these analyses three factors emerge as potentially related to huillin distribution, and further elucidation of these are suggested as priorities for research to underpin the species' conservation. These factors are: a) the distribution of crustacean prey, with absence of huillin from one river basin and from mountainous streams correlated with low densities of crustaceans in these places; b) human habitation, which may explain why huillin dispersed southwards, but not northwards, from the main lake, although underwater visibility may also be relevant; c) the presence of the introduced American mink Mustela vison, because although there was a positive relationship between the occurrence of mink and huillin in Lake Nahuel Huapi, there was a negative relationship in their occurrence between other lakes. We discuss possible explanations for all three factors.

The extent to which anti-predator mobbing can be modified in response to new predators was investigated by examining the response of terns (Sterna hirundo and S. paradisaea) and gulls (Larus fuscus, L. argentatus and L. canus) to introduced mink Mustela vison, native otter Lutra lutra and rabbit Oryctolagus cuniculus models in areas inhabited by mink and areas uninhabited by mink. Gulls and terns typically flock over predators of adult birds (a fleeing response), whilst diving at predators of chicks and eggs (an attacking response). Terns in mink-inhabited areas flocked over a model of a mink, but did not dive at it as much as they dived at otter and rabbit models. A stronger fleeing rather than attacking response suggests that adult terns perceive mink as a threat to themselves as well as to their chicks and eggs. Gulls, in comparison, dived at the mink model, indicating that mink are not perceived as a threat to the adults of these considerably larger species. Both gulls and terns showed a much lower level of response to mink in mink-free areas, suggesting that the type and extent of mobbing is altered through experience with predators and the level of risk associated with mobbing the predator.

Patterns of habitat selection by American mink Mustela vison within foraging areas located on the shore, were studied in a coastal environment of Scotland from November to March in 1983/84, 1984/85 and 1994/95. The abundance of prey in the intertidal zone was modelled in relation to abiotic environmental characteristics. Four factors were found to be important predictors of prey abundance: the position within the tidal zone, the abundance and size of rockpools, the nature of the substratum and the presence of fresh water streams. The model was used to predict prey abundance in different areas of the shore. We then investigated whether mink were choosing areas with higher prey abundance at different tidal levels and within, as opposed to between, core areas (areas with a relatively high density of fixes, encompassing usually one or more dens). Only when foraging at low or mid-tide and within core areas were mink found to behave selectively. They showed no significant preference for areas rich in prey when foraging at high tide and between core areas. Mink were also found to avoid areas with fresh water streams and to prefer foraging in the mid-tide zone. The findings are discussed in relation to prey abundance and competition with the otter Lutra lutra.

Body sizes of European mink (Mustela lutreola L.), polecat (M. putorius L.) and American mink (M. vison Schreber) were studied over a 10-year period in an area of north-eastern Belarus, before and after the invasion by American mink, and data are presented on interspecific interactions. On arrival in the study area American mink males were larger than males of European mink and polecat, and American mink females were larger than females of the other species. After arrival of the American mink its mean body size decreased, whilst the resident male and female European mink and female polecat increased as measured in absolute mass, length and relative mass. The observations suggest a strong character convergence most plausibly explained as a response to the invading exotic by the residents as well as in the invading species itself, whilst a divergence had been expected. There was no evidence to show whether these differences were genetically based. The body size data are consistent with the hypothesis that European mink, and to a lesser extent polecat, are responding to direct aggression from American mink (rather than merely competing for resources), with the smaller individual European mink being more likely to disappear first. We provide direct evidence for the aggressive nature of inter-specific relations from observations using radio-tracking: all observed inter-specific interactions were aggressive, significantly more so than intraspecific encounters, causing the European mink to flee, and several left the study area altogether. Implications for niche theory and for conservation management are discussed.

The abundance of mink, otter, and polecat may be inferred from records of their scats, and the feeding biology of the species is often studied by analysis of skeletal remains and other hard parts in faeces. However, in some situations it is difficult to distinguish between faeces from these three mustelid species. A method is described for assigning faeces to these three mustelid species, based on analysis of DNA extracted from their scats. Mustelid-specific primers were developed for PCR amplification of a part of the mitochondrial cytochrome b gene, and two restriction enzymes were found to detect species-specific sequence variation. Analysis of DNA from different faecal samples showed that the results were reproducible and that the approach provided an efficient method of species identification.