Feeding habits of invasive American mink (Neovison vison) in northern Germany—potential implications for fishery and waterfowl

In order to collect ecological data of invasive American mink (Neovison vison) at a fishpond area in northeastern Germany, we conducted a telemetry study in which 14 mink were radio-tracked. During this project, 2,502 scats from radio-tracked individuals were collected in the period from October 2003 to October 2005. Investigated mink principally prey on fish, small mammals and birds (eggs inclusive), whereas amphibians, reptiles and invertebrates were caught infrequently. Analysing mink scats of different seasons, we found significant seasonal variations of diet composition. In spring, fish, mammals and birds were hunted in similar amounts. During summer, birds made up the main part of the diet followed by mammals. In autumn, the proportion of birds in the mink diet decreased, whereas fish gained in importance. This trend continued during the winter period, when mink preyed almost exclusively on fish. Amphibians, crustaceans, insects, molluscs and reptiles were found only occasionally in scat samples. Among birds, the mink preyed mainly on the Eurasian Coot (Fulica atra) followed by the Mallard (Anas platyrhynchos). Mammalian prey was clearly dominated by the water vole (Arvicola terrestris) and among fish, mink hunted especially perch (Perca fluviatilis), roach (Rutilus rutilus) and carp (Cyprinus carpio). Results clearly demonstrate that mink is an opportunistic predator, which hunts its prey according to availability and vulnerability, respectively. Despite the high portions of fish in their autumn and winter diet, the economic damage caused by mink seems to be negligible. However, high predation rates on birds during the breeding season indicate a potential negative impact of mink on waterfowl.     

Habitat selection as a hierarchical spatial process: the green woodpecker at the northern edge of its distribution range

Habitat selection can be envisaged as a hierarchical spatial process, from choice of home range to choice of dietary item. The green woodpecker (Picus viridis) is described as being closely bound to cultivated land and deciduous forests, mainly due to its summer diet composed of ants (Hymenoptera: Formicidae) found on meadows and pastures. To explore possible responses of this woodpecker to recent changes in land use practice, we studied home ranges, feeding habitats and food selection of a marginal population (four radio-marked males and five females) in a 30,000-ha conifer-dominated landscape at the northern edge of its distribution range in south-central Scandinavia. We asked: (1) Is the green woodpecker confined to areas with cultivated land and deciduous forest? (2) If so, are important food items (ants) particularly abundant or exclusively found there? (3) Can clearcuts and young plantations substitute for cultivated land as feeding habitat? Home ranges (mean=100 ha) were invariably confined to the parts of the landscape that contained cultivated land (<1% of the total area). In summer, birds preferred to feed in cultivated land, presumably due to a higher overall biomass of ants compared to forest habitats. They avoided clearcuts, but preyed extensively upon soil-dwelling ants in young conifer stands (16–30 years old). We failed to find preferences for particular ant groups (Lasius niger and L. flavus) associated with cultivated land. The principal summer food was Serviformica, an ant group that was equally abundant in cultivated land and forest habitat. A positive correlation between ant body mass and a preference index suggests that the birds selected the larger ant species independent of habitat type. In winter, birds fed exclusively on mound-building Formica rufa-ants in closed-canopy, older forest stands. Our results indicate that the green woodpecker successfully utilizes young conifer plantations as feeding habitat. At a larger scale, we hypothesize that green woodpecker populations fail to establish in managed forest tracts, not because of food shortage, but because the landscapes lack cultivated land serving as a key stimulus encouraging individuals to settle.     

Habitat- and sex-related differences in a small carnivore’s diet in a competitor-free environment

The alien invasive American mink Neovison vison is fully established in the low species richness and competitor-free environment of Iceland. This study documents the diversity as well as seasonal and sexual variation in the diet of mink in Iceland based on stomach contents. Seasonal changes mainly reflected variation in abundance of migratory birds and wood mice Apodemus sylvaticus. In comparison with mink elsewhere in similar habitats, the mink in Iceland consumed more fish and birds and fewer mammals, which is in accordance with local availability. This reinforces evidence of opportunistic foraging. Females generally ate more fish and fewer birds than males and this might be explained by their smaller body size and possible limitation in catching larger birds. Mink in coastal habitats showed greater sexual differences in diet than mink in riparian habitats, probably reflecting less prey diversity in riparian habitats than coastal ones. This study is an input towards explaining the ecological consequences of sexual size dimorphism and supports the hypothesis that generalist species might be successful invaders due to their capability in utilising new and diverse resources. The mink in Iceland can be regarded as a model for a small-bodied semi-aquatic carnivore away from the confounding effects of inter-specific competition.     

Use of a barbed tool by an adult and a juvenile woodpecker finch (Cactospiza pallida)

Here we describe the modification and use of a new tool type in the woodpecker finch (Cactospiza pallida). This species is known to habitually use twigs or cactus spines to extract arthropods out of tree holes. We observed an adult and a juvenile bird using several barbed twigs from introduced blackberry bushes (Rubus niveus) which the adult bird had first modified by removing leaves and side twigs. The barbs of blackberry tools provide a novel functional feature not present in tools made from native plants and de-leafing of twigs never has been observed before. Both birds were observed using several of these tools to extract prey from under the bark of the native scalesia tree (Scalesia penduculta). They oriented the twigs such that the barbs pointed towards themselves; this rendered the barbs functional as they could be used to drag prey out of a crevice. The juvenile bird first watched the adult using the tool and then used the tool that the adult bird had left under the bark at the same location and in the same way as the adult. Our observation highlights the fact that opportunities for the transmission of social information do occur in the wild and indicates that woodpecker finches are flexible in their choice of tool material and tool modification.     

Corynosoma strumosum (Acanthocephala) infection in marine foraging mink (Neogale vison) and river otter (Lontra canadensis) and associated peritonitis in a juvenile mink

Corynosoma strumosum (Acanthocephala), a widespread parasite of pinnipeds, is reported in marine foraging North American mink (Neogale vison) and river otter (Lontra canadensis) on Vancouver Island, British Columbia. This is the first confirmed case of infection by C. strumosum in river otters on the west coast of North America and may be the first confirmed case of infection in wild North American mink; C. strumosum has previously been reported in river otters in Europe (Lutra lutra) and in farmed mink fed with marine fish. We also detected a case of acanthocephalan associated peritonitis in a juvenile mink. Furthermore, though infections with Corynosoma spp. are often assumed to be accidental in mustelids, some C. strumosum individuals found in mink showed signs of reproductive activity. These findings indicate that mink may be a competent definitive host and represent a reservoir in coastal habitats although further research is needed to confirm this. Investigating whether river otters may be competent hosts and determine the prevalence of infection in coastal populations would determine the potential implications of C. strumosum for coastal otters and minks. Our report indicates that mink and possibly river otter living in coastal areas are vulnerable to this previously unreported parasitic infection with mortality risk, at least in juvenile individuals.     

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.     

SNP markers associated with body size and pelt length in American mink (<Emphasis Type="Italic">Neovison vison</Emphasis>)

Background

Identification of genes underlying production traits is a key aim of the mink research community. Recent availability of genomic tools have opened the possibility for faster genetic progress in mink breeding. Availability of mink genome assembly allows genome-wide association studies in mink.

Results

In this study, we used genotyping-by-sequencing to obtain single nucleotide polymorphism (SNP) genotypes of 2496 mink. After multiple rounds of filtering, we retained 28,336 high quality SNPs and 2352 individuals for a genome-wide association study (GWAS). We performed the first GWAS for body weight, behavior, along with 10 traits related to fur quality in mink.

Conclusions

Combining association results with existing functional information of genes and mammalian phenotype databases, we proposed WWC3, MAP2K4, SLC7A1 and USP22 as candidate genes for body weight and pelt length in mink.

     

On the phylogenetic position of the Okinawa woodpecker (Sapheopipo noguchii)

The Okinawa woodpecker Sapheopipo noguchii is the rarest extant woodpecker species. The monotypic genus Sapheopipo was considered to be a representative of an old lineage of woodpeckers that led to the Eurasian genera Picus and the Blythipicus–Gecinulus species. This view, based on similarities in color patterns, external morphology and foraging behavior, has been adopted in all major accounts of the family. The alternative view, that this woodpecker may be related to the widespread white-backed woodpecker Dendrocopos leucotos, which evolved distinctive subspecies on other East Asian islands, has not been generally accepted. We analyzed partial sequences of the mitochondrial cytochrome b (cyt b) gene to test these hypotheses. The data suggest that the Okinawa woodpecker is a member of the genus Dendrocopos, with white-backed woodpecker and great spotted woodpecker D. major as close relatives. Color patterns support the genetic results and indicate a closer relationship with the white-backed woodpecker. Consequently, the correct taxonomic designation of the Okinawa woodpecker would be Dendrocopos noguchii (Seebohm in Ibis 5(5):173–182, 1887) in the tribe Campetherini rather than Picini.This revised version was published online in February 2005 with corrections to tables 1 and 2.     

The ecology of tool-use in the woodpecker finch (Cactospiza pallida)

Insects, mammals and birds are known to use tools, but empirical evidence of the ecological importance of tool‐use is scarce. Here, we present the first ecological study of tool‐use by a bird species. Woodpecker finches use twigs or cactus spines to pry arthropods out of tree‐holes. We compared tool‐use during wet and dry seasons in two different vegetation zones: the Arid Zone and the humid Scalesia Zone. In the Scalesia Zone, where food was abundant and easily accessible, woodpecker finches rarely used tools. In contrast, in the Arid Zone, where food was limited and hard to access, they obtained half of their prey using tools during the dry season. Tool‐use enabled the birds to reach particularly large and otherwise inaccessible prey hidden in tree‐holes. Our data suggest that tool‐use in the woodpecker finch has evolved in response to the dry and unpredictable conditions in the coastal zone of the Galápagos Islands.     

The white-backed woodpecker: umbrella species for forest conservation planning?

In northern Europe, a long history of land use has led to profound changes within forest ecosystems. The white-backed woodpecker (Dendrocopos leucotos) is one of several specialised forest species whose populations have declined. Conservation management directed at this species’ habitat has made it a de facto umbrella species for conservation of the biodiversity associated with forests rich in deciduous trees and dead wood. We assessed empirically the value of the white-backed woodpecker as an indicator and umbrella species in central Sweden. Occurrence of the woodpecker in breeding bird atlas squares (5 × 5 km²) indicated high species richness of forest birds, particularly species of special conservation concern, which included on average 13% more species in squares with than without the woodpecker. The number of red-listed cryptogam species expected to benefit from conservation actions directed at white-backed woodpecker habitats was higher in squares where the woodpecker bred compared to where is was absent. However, no such pattern was found for red-listed beetles, a group with very few records in the studied squares. White-backed woodpecker occurrence was positively associated with the current area of deciduous and mixed forest of high conservation value. Considering its indicator value, its specialised habitat requirements and its potential as a communication tool, using the white-backed woodpecker as an umbrella species may provide a coarse filter for the conservation of several other deciduous forest species. However, focusing solely on white-backed woodpecker habitat may not provide for the conservation of all such species, which stresses the need for a suite of complementary planning approaches.     

Temporal dynamics of woodpecker predation on emerald ash borer (Agrilus planipennis) in the northeastern U.S.A.

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Quantifying the Impact of Woodpecker Predation on Population Dynamics of the Emerald Ash Borer (Agrilus planipennis)

The emerald ash borer (EAB), Agrilus planipennis, is an invasive beetle that has killed millions of ash trees (Fraxinus spp.) since it was accidentally introduced to North America in the 1990s. Understanding how predators such as woodpeckers (Picidae) affect the population dynamics of EAB should enable us to more effectively manage the spread of this beetle, and toward this end we combined two experimental approaches to elucidate the relative importance of woodpecker predation on EAB populations. First, we examined wild populations of EAB in ash trees in New York, with each tree having a section screened to exclude woodpeckers. Second, we established experimental cohorts of EAB in ash trees in Maryland, and the cohorts on half of these trees were caged to exclude woodpeckers. The following spring these trees were debarked and the fates of the EAB larvae were determined. We found that trees from which woodpeckers were excluded consistently had significantly lower levels of predation, and that woodpecker predation comprised a greater source of mortality at sites with a more established wild infestation of EAB. Additionally, there was a considerable difference between New York and Maryland in the effect that woodpecker predation had on EAB population growth, suggesting that predation alone may not be a substantial factor in controlling EAB. In our experimental cohorts we also observed that trees from which woodpeckers were excluded had a significantly higher level of parasitism. The lower level of parasitism on EAB larvae found when exposed to woodpeckers has implications for EAB biological control, suggesting that it might be prudent to exclude woodpeckers from trees when attempting to establish parasitoid populations. Future studies may include utilizing EAB larval cohorts with a range of densities to explore the functional response of woodpeckers.     

Do increases in the availability of standing dead trees affect the abundance,nest-site use,and niche partitioning of great spotted and middle spotted woodpeckers in riverine forests?

Standing dead trees may be a limited resource for woodpeckers in managed forests, especially for species that rely on dead wood for their nest or roost cavity, and as foraging sites. Effective conservation strategies for woodpeckers require a detailed knowledge of species’ responses to dead wood availability. To investigate the importance of standing dead wood (snags) for the abundance and nest-site use of the great spotted woodpecker Dendrocopos major and middle spotted woodpecker Leiopicus medius in mature riverine forests, we compared the responses of birds between two periods—before mass mortality, and during a pulse in standing dead trees. The density of standing dead trees available for cavity excavation by the great spotted woodpecker and the middle spotted woodpecker increased significantly during the study period: 37-fold and 4-fold, respectively. Temporal trends in the abundance of both woodpecker species from 2000 to 2015 were not significant. Great spotted woodpeckers were significantly more likely to use dead trees and places with wounds in species other than oak and ash during the outbreak period than in the pre-outbreak period. Middle spotted woodpeckers were significantly less likely to excavate cavities in tree species other than oak and ash in the outbreak period, but dead trees were more likely selected. An interspecific comparison suggests that the probability of a nest-hole having been excavated by a middle spotted woodpecker increased with a nest-hole sited in ash, in a dead tree, in a limb/branch, and decreased with a nest-hole in a closed forest. These findings suggest that woodpecker species, especially weak excavators, may benefit from an increase in dead wood availability leading to nest niche shifts into more favorable substrates for cavity excavation. However, a strong increase in dead wood availability does not modify the general pattern of niche partitioning between great spotted and middle spotted woodpeckers. Conservation plans for the specialized middle spotted woodpecker must consider the preference for dead and decaying trees. The decreasing number of large ashes and oaks, and the lack of natural regeneration of the latter species, may negatively affect the middle spotted woodpecker in the future.     

Influence of dietary sources of fat on lipid synthesis in mink (Mustela vison) mammary tissue

• 1.1. The fatty acid composition of the triglyceride fraction of mink milk sampled during mid-lactation (day 28 post partum) from two nursing mink was compared to that of plasma samples and to the fatty acid composition of the feed rations used.
• 2.2. Chemical analysis of the triglyceride composition of mink milk demonstrated only minute concentrations of fatty acids with a chain length below C₁₄.
• 3.3. The saturated C_16:0- and C_18:0-unit fatty acids in mink milk made up for 24–40% of the total amount of fatty acids extracted, the remainder being represented by mono and polyunsaturated long-chain (C₁₆-C₂₄) fatty acids.
• 4.4. Preliminary in vitro experiments proved the incorporation of¹⁴C-labelled glucose, acetate or palmitate into triacylglycerols in cultures of mink mammary tissue to be linear for at least 2 hr.
• 5.5. The in vitro capacity for de novo fatty acid synthesis in mink mammary tissue using 14C-labelled glucose or acetate was low, i.e. ranging from 0.096–0.109 nmol/g (fresh tissue)/min, and amounted to only about 5% of that obtained in the case of [¹⁴C]palmitic acid incubation.
• 6.6. Following ¹⁴C-labeIled acetic or palmitic acid incubation of mink mammary tissue neither desaturation nor chain elongation was observed.
• 7.7. In response to long-term feeding on rations with two different sources of animal fat (F = fish oil or L = lard) the influence of compositional changes in dietary neutral lipids on the fatty acid composition of the lipids of mink milk is discussed.

     

Effects of Dietary Copper on Nutrient Digestibility,Tissular Copper Deposition and Fur Quality of Growing-Furring Mink (Mustela vison)

The present study investigated the effects of dietary copper (Cu) on growth performance and fur quality in growing-furring minks. One hundred and five standard dark female minks were randomly assigned to seven groups with the following dietary treatments: basal diet with no supplemental Cu (control) and basal diet supplemented with either 6, 12, 24, 48, 96 or 192 mg/kg Cu from copper sulphate, respectively. Our data showed that final body weight (P?=?0.033), daily gain (P?=?0.029) and fat digestibility (P?=?0.0006) responded to increasing levels of Cu. The activity of glutamic-oxalacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) in serum increased (linear and quadratic, P?<?0.05) as Cu increased in the diet. Increasing Cu improved total protein (TP) and albumin (ALB) (quadratic, P?<?0.05). The level of ceruloplasmin (CER) responded in a linear (P?<?0.0001) and quadratic (P?<?0.0001) form with increasing level of Cu. Colour intensity of those minks pelted suggested that relatively high levels of supplemental Cu have a beneficial effect on intensifying hair colour of dark mink but did not affect leather thickness. Liver Cu and plasma Cu concentrations of the mink linearly (P?<?0.0001) responded to increasing levels of Cu. Our results indicate that growing-furring mink can efficiently utilize added dietary fat and that Cu plays an important role in the digestion of dietary fat in growing-furring mink, and supplemental dietary Cu in growing-furring mink promotes fat digestion and improve hair colour.     

Visual fields in woodcocks Scolopax rusticola (Scolopacidae; Charadriiformes)

Woodcocks, Scolopax rusticola, are long-billed terrestrial wading birds (Scolopacidae; Charadriiformes) which forage primarily by probing in soft substrates for invertebrates. Visual field topography in restrained alert birds was investigated using an ophthalmoscopic reflex technique.

1. Eye movements of significant amplitude are absent.
2. The retinal binocular field is long and narrow. It extends through 190° in the median sagittal plane. When the head adopts a normal posture (bill at an angle of 40° below the horizontal) the binocular field stretches from 25° above the bill to 5° above the horizontal behind the head. Thus, woodcocks have comprehensive visual coverage of the hemisphere above them but the bill falls outside the visual field. Maximum binocular field width equals 12° and occurs perpendicular to the line of the bill. To the rear of the head binocular field width is less than 5° except in an area 40° above the horizontal where it increases to 7°.
3. Monocular retinal fields in the horizontal plane are 182° wide. There is no blind sector at the margin of the optical fields.
4. The general structure of woodcock skulls facilitates panoramic vision in a horizontal plane.
5. Interspecific comparisons are consistent with the hypothesis that visual field topography among birds is closely associated with the role of vision in foraging. Comprehensive visual coverage of the celestial hemisphere probably occurs only in species, such as woodcocks, which rely primarily upon senses other than vision to guide foraging.

     

A re-assigned American mink (Neovison vison) map optimal for genome-wide studies

Our previously published second generation genetic map for the American mink (Neovison vison) has been used and redesigned in its best for genome-wide studies with maximum of efficiency. A number of 114 selected markers, including 33 newly developed microsatellite markers from the CHORI-231 mink Bacterial Artificial Chromosome (BAC) library, have been genotyped in a two generation population composed of 1200 individuals. The outcome reassigns the position of some markers on the chromosomes and it produces a more reliable map with a convenient distance between markers. A total of 104 markers mapped to 14 linkage groups corresponding to the mink autosomes. Six markers are unlinked and four markers are allocated to the X chromosome by homology but no linkage was detected. The sex-average linkage map spans 1192 centiMorgans (cM) with an average intermarker distance of 11.4 cM and 1648 cM when the ends of the linkage groups and the autosomal unlinked markers are added. Sex-specific genetic linkage maps were also generated. The male sex-specific map had a total length of 1014.6 cM between the linked markers and an average inter-marker interval of 9.7 cM. The female map has a corresponding length of 1378.6 cM and an average inter-marker interval of 13.3 cM. The study is complemented with additional anchorage for most of the chromosomes of the map by BAC in situ hybridization with clones containing microsatellites strategically selected from the various parts of the genome. This map provides an improved tool for genetic mapping and comparative genomics in mink, also useful for the future assembly of the mink genome sequence when this will be taken forward.     

Indirect genetic effects contribute substantially to heritable variation in aggression-related traits in group-housed mink (Neovison vison)

Background

Since the recommendations on group housing of mink (Neovison vison) were adopted by the Council of Europe in 1999, it has become common in mink production in Europe. Group housing is advantageous from a production perspective, but can lead to aggression between animals and thus raises a welfare issue. Bite marks on the animals are an indicator of this aggressive behaviour and thus selection against frequency of bite marks should reduce aggression and improve animal welfare. Bite marks on one individual reflect the aggression of its group members, which means that the number of bite marks carried by one individual depends on the behaviour of other individuals and that it may have a genetic basis. Thus, for a successful breeding strategy it could be crucial to consider both direct (DGE) and indirect (IGE) genetic effects on this trait. However, to date no study has investigated the genetic basis of bite marks in mink.

Result and discussion

A model that included DGE and IGE fitted the data significantly better than a model with DGE only, and IGE contributed a substantial proportion of the heritable variation available for response to selection. In the model with IGE, the total heritable variation expressed as the proportion of phenotypic variance (T²) was six times greater than classical heritability (h²). For instance, for total bite marks, T² was equal to 0.61, while h² was equal to 0.10. The genetic correlation between direct and indirect effects ranged from 0.55 for neck bite marks to 0.99 for tail bite marks. This positive correlation suggests that mink have a tendency to fight in a reciprocal way (giving and receiving bites) and thus, a genotype that confers a tendency to bite other individuals can also cause its bearer to receive more bites.

Conclusion

Both direct and indirect genetic effects contribute to variation in number of bite marks in group-housed mink. Thus, a genetic selection design that includes both direct genetic and indirect genetic effects could reduce the frequency of bite marks and probably aggression behaviour in group-housed mink.     

Diet of free-ranging American mink and European polecat in Denmark

Stomach and intestine contents of 211 American minkMustela vison Schreber, 1777 from two areas (Thy and Bornholm) in Denmark and stomach contents of 47 polecatsM. putorius Linnaeus, 1758 from Thy were analysed. Sympatric mink (from Thy) preyed mostly on mammals (55% occurrence), followed by amphibians (36%), birds (33%) and fish (30%), whereas polecat preyed mostly on amphibians (87%) and mammals (34%), and only occasionally on birds (9%) and fish (6%). Allopatric mink (from Bornholm) preyed mostly on birds (50%), followed by mammals (42%), fish (25%) and amphibians (4%). With the possible exception of some amphibians, no endangered species were found in their diet. No differences were found in food composition between wild and escaped farm mink. The concern that mink in general might have a detrimental effect on its prey species and other mustelids in terms of food competition in Denmark may be unjustified. It cannot be ruled out, however, that mink may locally have a seriously negative effect on some specific prey species, and clearly, more data is needed on eg prey abundance and spring and summer mink diet, to make stronger conclusions.