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Datasheet

Ondatra zibethicus (muskrat)

Summary

  • Last modified
  • 13 July 2018
  • Datasheet Type(s)
  • Invasive Species
  • Natural Enemy
  • Host Animal
  • Preferred Scientific Name
  • Ondatra zibethicus
  • Preferred Common Name
  • muskrat
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Chordata
  •       Subphylum: Vertebrata
  •         Class: Mammalia
  • Summary of Invasiveness
  • Ondatra zibethicus is an amphibious rodent which is native to North America but has been introduced for its fur to much of Europe, as well as parts of Asia and South America. It inhabits wetlands, where it dama...

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Pictures

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PictureTitleCaptionCopyright
Adult Muskrat feeding; Piper Point Regional Park, Burnaby, British Columbia, Canada.
TitleAdult feeding
CaptionAdult Muskrat feeding; Piper Point Regional Park, Burnaby, British Columbia, Canada.
Copyright©Alan D. Wilson/www.naturespicsonline.com
Adult Muskrat feeding; Piper Point Regional Park, Burnaby, British Columbia, Canada.
Adult feedingAdult Muskrat feeding; Piper Point Regional Park, Burnaby, British Columbia, Canada.©Alan D. Wilson/www.naturespicsonline.com

Identity

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Preferred Scientific Name

  • Ondatra zibethicus L., 1766

Preferred Common Name

  • muskrat

Other Scientific Names

  • Castor zibethicus
  • Fiber zibethicus
  • Mus zibethicus
  • Myocastor zibethicus
  • Ondatra americana Tiedemann, 1808
  • Ondatra zibethica

International Common Names

  • English: marsh hare; marsh rabbit; musquash; swamp rabbit

Local Common Names

  • Denmark: Bisamrotte
  • Estonia: ondatra; piisamrott
  • Finland: piisami
  • Germany: Biberratte; Bisam; Bisambiber; Bisamratte; Moschusratte; Muschmaus; Sumpfhase; Sumpfkaninchen; Wasserratte; Zibethratte; Zibetmaus; Zwergbiber
  • Iceland: moskusrotta
  • Latvia: bizamžurka; ondatra
  • Lithuania: ondatra
  • Poland: pizmak
  • Russian Federation: ondatra

Summary of Invasiveness

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Ondatra zibethicus is an amphibious rodent which is native to North America but has been introduced for its fur to much of Europe, as well as parts of Asia and South America. It inhabits wetlands, where it damages vegetation (for food and for building its lodges), banks and other structures (by burrowing), and neighbouring crops, and can threaten populations of a variety of native species. It is recommended for eradication by the Bern Convention on the Preservation of European Wild Plants and Animals and their Natural Habitats (Bern Convention Standing Committee, 1999), and is listed by DAISIE as one of the 100 worst invasive species in Europe (DAISIE, 2011), but its high rate of reproduction makes it difficult to control.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Chordata
  •             Subphylum: Vertebrata
  •                 Class: Mammalia
  •                     Order: Rodentia
  •                         Family: Muridae
  •                             Subfamily: Microtinae
  •                                 Genus: Ondatra
  •                                     Species: Ondatra zibethicus

Notes on Taxonomy and Nomenclature

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No subspecies or populations are described for Europe, although Errington (1961) considered the existence of 16 ‘forms’.

The order is characterized by a single pair of upper incisors and two groups of two pairs of teats. The genus Ondatra is close to Microtus and it can be suggested that this genus is derived from Microtus.

Description

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O. zibethicus is an amphibious rodent with a broad head and short ears. Its fur is of variable colour from grey to brown on the back, while the lower parts are lighter coloured. The fur is dense and waterproof resulting in a high degree of buoyancy. The tail is scaled, nearly nude and laterally flattened; it helps the animal to swim and fight. Well adapted to a semi-aquatic life, O. zibethicus can close its nose, ears, and mouth, so as to swim easily under water. When swimming, the body emerges from water and the tail acts as a rudder. Both sexes have perineal musk glands, the reason for the common name of the species. Males have a penial bone.

Total length: 46-67 cm (tail: 20-27 cm); weight: 0.6-2 kg.

The droppings have an elongated form, and are brown or black. They are usually deposited in a pile. They measure 10-12 mm in length with a diameter of 4-5 mm. Tracks through vegetation are about 10 cm wide.

Distribution

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The natural range of O. zibethicus is throughout most of the United States and Canada, and in parts of northern Mexico (Long, 2003). The species has been introduced to Europe, parts of northern, central and eastern Asia, and Tierra del Fuego.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

ChinaLocalisedIntroducedLong, 2003
JapanLocalisedIntroducedLong, 2003
KazakhstanWidespreadIntroducedLong, 2003
KyrgyzstanWidespreadIntroducedLong, 2003
MongoliaPresentIntroducedLong, 2003
UzbekistanPresentIntroducedLong, 2003

North America

CanadaWidespreadNativeLong, 2003
MexicoLocalisedNativeLong, 2003
USAWidespreadNativeLong, 2003

South America

ArgentinaLocalisedIntroducedAnderson et al., 2006
ChileLocalisedIntroducedLong, 2003

Europe

AustriaWidespreadIntroduced1914 Invasive Niethammer and Krapp, 1982; NOBANIS, 2011
BelgiumWidespreadIntroduced1925 Invasive Niethammer and Krapp, 1982
BulgariaPresentIntroduced1956Peshev, 1996
Czechoslovakia (former)WidespreadIntroduced1905 Invasive Niethammer and Krapp, 1982
DenmarkLocalisedIntroducedBirnbaum, 2006; NOBANIS, 2011
EstoniaPresentIntroduced1947Birnbaum, 2006; NOBANIS, 2011
FinlandPresentIntroduced1919 Invasive Danell, 1996
FranceWidespreadIntroduced1928 Invasive Niethammer and Krapp, 1982
GermanyWidespreadIntroduced1914 Invasive Niethammer and Krapp, 1982
HungaryWidespreadIntroduced1915Niethammer and Krapp, 1982
IrelandEradicatedIntroduced1927Danell, 1996
LatviaLocalisedIntroduced1961 Not invasive Birnbaum, 2006; NOBANIS, 2011
LithuaniaLocalisedIntroduced1954NOBANIS, 2011Potentially invasive
NetherlandsWidespreadIntroduced1968 Invasive Doude van Troostwijk, 1978
NorwayPresent, few occurrencesIntroduced1969 Invasive Danell, 1996
PolandWidespreadIntroduced1924Institute and of Nature Conservation, Polish Academy of Sciences, 2012Originally invasive; now declining but still found throughout country.
RomaniaPresentIntroduced1942Niethammer and Krapp, 1982
Russian FederationPresentIntroduced1928 Invasive Danell, 1996
SwedenLocalisedIntroduced1946 Invasive Danell, 1996
SwitzerlandWidespreadIntroduced1930Birnbaum, 2006
UKEradicatedIntroduced1927Danell, 1996
UkrainePresentIntroduced1944Long, 2003
Yugoslavia (former)PresentIntroduced1932 Invasive Niethammer and Krapp, 1982

History of Introduction and Spread

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O. zibethicus was first introduced to Europe in 1905 near Prague (Niethammer and Krapp, 1982). As early as 1906, different European countries tried to limit its expansion because there was no natural obstacle to its expansion. Deliberate introductions are reported from Finland (1920), Russia (1927) and Lithuania, Bulgaria in 1956 (Peshev, 1996), from Japan and Mongolia (Long, 2003), and also from France, Belgium and Poland.

Nowadays, it is present from eastern Scandinavia (Finland and northern Sweden) to France and Eastern Europe. It is absent in Spain, Portugal, Italy and Greece. It is found throughout most of Russia, including Siberia, and has spread from Russia and Mongolia into northern China (Long, 2003).
 
In South America, it was introduced to Tierra del Fuego by the Argentine government during the 1940s and 1950s to develop fur exploitation and it currently has a widespread distribution in the archipelago (Anderson et al., 2006).

Habitat

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O. zibethicus lives mostly in freshwater, along riverbanks with slow moving waters, and in lakes, ponds, and wetlands. In northern countries it needs a water depth of between 1 and 2 m to prevent the water freezing completely and to allow vegetation growth.

Animals can be found in dikes along roads if they contain enough water and if the banks are compact enough to allow the digging of burrows. O. zibethicus can create two types of habitation: burrows in river banks, or lodges. Both seem to have the same ecological role and are used according to the local conditions. However, in most cases, animals occupy burrows in summer and lodges in winter. They usually build lodges out of reeds and other local vegetation (Typha, Iris, Carex, Juncus). Lodges are used for protection against the cold, but can also be used for food at the end of the winter – the material from which the lodge is made may be eaten if food is short. They may be 8 to 10 feet across and 2 to 3 feet above water, with a single living chamber plus off-shoots, or several chambers. Both lodges and burrows have underwater entrances and above-water living quarters.
 
The spatial distribution of lodges and burrows is regular, indicating the territoriality of the species, even at low densities.
 
O. zibethicus is also able to live in estuaries and can survive in brackish or salty habitats (McConnell and Powers, 1995).
 
In a study in Oklahoma (USA), O. zibethicus were reported mostly in areas with favourable combinations of human population density, annual mean precipitation, abundance of major river drainage systems, and percentage cover of tall grass prairie and forested land cover (McDonald, 2006).
 
The average home range is between 7 to 70 meters and rarely do O. zibethicus explore distances greater than 150 meters from their lodge (Erickson, 1963, McConnell and Powers, 1995). They can be very territorial and return to their homes when experimentally removed for distances of 900 to 1800 m, even if this involves crossing roads (Erickson, 1963). Densities can be high, up to 30 pairs per ha (Errington, 1961)
 
Population density is generally 2-6 animals/ha in Sweden (Danell, 1977a; Zima, 1999) compared to 25-86 animals/ha in the USA (Errington, 1961, citing earlier work by the same author), but it can reach 50-60 animals/ha during peak years (Zima, 1999). Densities are highest and animals are largest, with the highest growth indices, in habitats with a supply of high quality food (Pankakoski, 1983).

Habitat List

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CategoryHabitatPresenceStatus
Brackish
Estuaries Secondary/tolerated habitat Harmful (pest or invasive)
Freshwater
Irrigation channels Principal habitat Harmful (pest or invasive)
Lakes Principal habitat Natural
Ponds Principal habitat Harmful (pest or invasive)
Ponds Principal habitat Natural
Reservoirs Principal habitat Harmful (pest or invasive)
Rivers / streams Principal habitat Harmful (pest or invasive)
Rivers / streams Principal habitat Natural
Littoral
Coastal areas Secondary/tolerated habitat Harmful (pest or invasive)
Terrestrial-natural/semi-natural
Riverbanks Principal habitat Harmful (pest or invasive)
Riverbanks Principal habitat Natural
Wetlands Principal habitat Harmful (pest or invasive)
Wetlands Principal habitat Natural

Biology and Ecology

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Reproductive biology

Breeding takes place from February to September in mild climates, but not before April in colder climates. After a gestation period of 28 to 30 days, the young are born blind, helpless and almost naked. After two weeks, their eyes open and after approximately eight weeks they are weaned.
 
Two to six litters are produced per year, the exact number varying geographically and depending on climatic conditions, food resources and population density (McVey et al, 1993, McConnell and Powers, 1995). Each litter contains six to seven young, occasionally nine; the number of young produced is correlated with territorial quality (Hjältén, 1991). The mortality of the offspring increases at low water temperatures and high population densities (cf. Meinert and Diemer 1977).
 
Female O. zibethicus are able to breed when five months old and males when seven months old (Heidecke and Seide, 1986). Both sexes are solitary when searching for territories. During the breeding season, they may form pairs, be polygamous or mate promiscuously (Le Boulangé, 1972; McVey et al., 1993).
 
Populations show cycles varying between 3 and 13 years in Canada; 4-year cycles were attributed to the 4-year cycle of the red fox Vulpes vulpes. However, social and trophic interactions are necessary to produce population dynamics and mink predation can modify density dependence and therefore the length of a cycle (Erb et al., 2000)
 
Behaviour
 
O. zibethicus is described as being mainly nocturnal with activity starting at dusk and ending at dawn. When it is not disturbed, it can show diurnal activity, dominated by feeding or bringing vegetation to its lodge. Well adapted for swimming, it spends most of its time in water or surrounding habitats.
 
Nutrition
 
Essentially herbivorous, O. zibethicus feeds mainly on Typha spp., Scirpus fluviatilis, Phragmites australis, Ponteredia cordata (North America), or Nymphaea spp., but sometimes it can feed on crops such as carrots or grains, or on fruit or bark. Some populations seem to be omnivorous, preying on freshwater mussels or crayfish, or eating carrion such as fishes, invertebrates, small fishes, frogs or even carcasses of other muskrats. Animal prey seems to increase in the diet when preferred plant species are scarce (Triplet, 1983). O. zibethicus were found not to prey on clams Anodonta anatina smaller than 50 mm; the optimal size is between 60 and 90 mm (Jokela and Mutikainen, 1995)
 
During winter O. zibethicus feeds on roots and shoots dug from marsh bottoms, and twigs, buds and bark of various trees, including willows (Salix), cottonwoods (Populus), ash (Fraxinus) and box elders (Acer negundo). According to research cited by Kadlec et al. (2007), as a mean, each animal has to eat 82 g dry biomass per kg of body mass per day, and cattail (Typha spp.) can support seven times as many animals as an equal amount of bulrush (Scirpus spp.).
 
O. zibethicus eats about 2% of the annual net primary production of a wetland, but their lodges represent about 20% (research cited by Kadlec et al., 2007). Extrapolating, twenty animals per ha may utilize 1750 kg/ha year, which is a large fraction of the macrophyte standing crop.

Climate

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ClimateStatusDescriptionRemark
C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
D - Continental/Microthermal climate Tolerated Continental/Microthermal climate (Average temp. of coldest month < 0°C, mean warmest month > 10°C)
Df - Continental climate, wet all year Preferred Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)
Ds - Continental climate with dry summer Tolerated Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Tolerated Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
68 55

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Bubo bubo Predator Adults/Juveniles not specific
Canis latrans Predator Adults/Juveniles not specific
Canis lupus Predator All Stages not specific
Circus aeruginosus Predator Adults/Juveniles not specific
Lutra lutra Predator Adults/Juveniles not specific
Lynx lynx Predator Adults/Juveniles not specific
Martes foina Predator Adults/Juveniles not specific
Mustela putorius Predator Adults/Juveniles not specific
Neovison vison Predator Adults/Juveniles not specific
Procyon lotor Predator Adults/Juveniles not specific
Vulpes vulpes Predator Adults/Juveniles not specific

Notes on Natural Enemies

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Predation by the Red Fox Vulpes vulpes occurs in lodges situated in shallow water close to the shore (Hjältén, 1991). Otters frequently feed on O. zibethicus during winter in Sweden (Skarén, 1993). Other predators are, in Europe, the Stone Marten Martes foina and the Polecat Mustela putorius, and in North America, American Mink Mustela vison, Fox Vulpes vulpes, Wolf Canis lupus, Coyote Canis latrans, Raccoon Procyon lotor, and Lynx Lynx lynx (Danell, 1996). In Northern European countries where the American Mink is widespread (for example in Poland), O. zibethicus seems to be declining (Brzezinski et al., 2010). Cases of predation on young individuals are also reported for the Eagle Owl Bubo bubo and Marsh Harrier Circus aeruginosus (Saunders, 1988; Link, 2005).

Means of Movement and Dispersal

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Young animals may have to find new territories. Movements are noticed during the autumn (varying according to the geographical location from August to November). Another movement occurs at the beginning of spring when individuals are searching for new territories. Movements are very dependent on the population density and on food resources. Precipitation can act as a favourable factor as flooded ground can facilitate movement. When they disperse, some animals can be seen trying to cross estuaries and cases of drowning have been reported.

Dispersal is the main component of range expansion. The spreading front moves at a rate ranging from 0.9 to 25.4 km/year, corresponding to a diffusion coefficient ranging from 51 to 230 km2/year (Danell, 1977b; Birnbaum, 2006; research cited by Kadlec et al., 2007). In France, the range expanded at a rate of 3300 km²/year in the 25 years prior to 1959 (Aubry, 1959).
 
Accidental introduction
 
It is obvious that some introductions were accidental, because animals could escape from fur farms. However, most introductions were intentional.
 
Intentional introduction
 
Intentional introduction is reported from the Czech Republic, France, Belgium and Poland. O. zibethicus was introduced to France around 1928 for breeding in captivity. The economic crisis of 1929 led to the closure of many fur farms, and animals were either released accidentally or intentionally. The main occurrences are dated 1933; by 1983, the whole country was occupied. Deliberate introductions are also reported from Finland (1920), Russia (1927) and Lithuania and Bulgaria (1956) (Peshev, 1996).
 
In South America, O. zibethicus was introduced to Tierra del Fuego by the Argentine government during the 1940s and 1950s to develop fur exploitation and it currently has a widespread distribution in the archipelago (Anderson et al., 2006).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Escape from confinement or garden escape Yes
Harvesting fur, wool or hair Yes

Impact Summary

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CategoryImpact
Economic/livelihood Negative
Environment (generally) Negative
Human health Negative

Economic Impact

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O. zibethicus can dig galleries in the banks of rivers, ponds and sewage plants. The banks are weakened by this and can break, causing flooding. Burrows have been reported as a threat to the security of dikes in The Netherlands (research cited by Kadlec et al., 2007), and they also create difficulties for vehicles travelling on the dikes.

The same problem can be seen in sewage treatment plants. O. zibethicus burrows in banks can be the cause of mixing waters of different qualities, reducing the functioning of the plant.
 
O. zibethicus can cause damage to railways, dams, dikes, and fish farms; they can chew through nets and fish traps. In Germany the costs of economic impacts caused by O. zibethicus are estimated to be 12,400,000 euros per year (Reinhardt et al., 2003).
 
O. zibethicus can create havoc with agriculture. Burghause (1988, 1996) reported that the species was particularly attracted by the tubers of Jerusalem artichoke (Helianthus tuberosus).

Environmental Impact

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Impact on habitats

O. zibethicus increases potential net nitrogen mineralization and nitrification rates. Their disturbance activities influence abiotic conditions, including soil nitrogen dynamics, which is an important component of wetland function (Connors et al. 2000). They alter invertebrate communities in wetlands, which affects food resources for wildlife and fish that feed on aquatic invertebrates in these habitats (De Szalay and Cassidy 2001).

An overabundance of O. zibethicus can modify the vegetal landscape (Kadlec et al., 2007). According to Burghause (1988), one animal is capable of cropping 1.5 m2 per night. When consuming rhizomatic plants, they can decrease biodiversity; as consumed species decrease and non-consumed ones (e.g. Carex) increase, the composition of the vegetation changes and reed beds can decline. Bernhardt and Schröpfer (1992) have shown that in the Ems region (Germany) O. zibethicus removes bulrushes (Typha latifolia), promoting the development of club-rushes (Scirpus lacustris). In such situations, insect communities and aquatic invertebrates could diminish because the opening up of reed beds could increase the possibilities for birds to feed, (see also Chashchukhin, 1987; Nummi et al. 2006; Danell 1996); this could be considered both as a negative and a positive effect.

Kadlec et al. (2007) reviewed literature on the effects of O. zibethicus on wetlands, with an emphasis on wetlands used for water treatment. O. zibethicus consume a small portion of the annual net primary productivity of the ecosystem, primarily rhizomes, but their mounds (lodges and feeding platforms) represent a significant share of this production (around 20%). Densities of 20 or more animals per hectare can destroy the majority of the macrophyte standing crop in a given year. Destruction of the wetland vegetative infrastructure may result in loss of some water quality parameters, but may not harm others. The integrity of berms may be threatened by burrowing. Impacts on wetland hydraulics are also possible. Loss of the emergent vegetation is viewed with dismay by owners and managers of treatment wetlands, regulators and the general public. Several case histories are reviewed by Kadlec et al. (2007) to illustrate the breadth and severity of muskrat damage in treatment wetlands. O. zibethicus control is given scant attention in existing treatment wetland literature, which provides very limited information on potential O. zibethicus problems, or the means to control them.

In Russia, there has been a reduction in edible plants and intensive growth of inedible plants which has been reported to cause a decrease in the number of O. zibethicus (Sokolov and Lavrov, 1993).

Impact on biodiversity

Abundance or more precisely overabundance of O. zibethicus can strongly threaten endemic species such as the Desman (Desmana moschata). It also impacts fishes and ground-nesting birds. Indirectly, through control operations, it could jeopardize populations of species such as the water vole Arvicola sapidus or even the otter Lutra lutra.

As well as crustaceans (such as crayfish), insects and bivalves such as zebra mussels (Dreissena polymorpha)(cf. Ulbrich, 1930; research cited in Danell, 1996), O. zibethicus sometimes feeds on threatened bivalve taxa such as Anodonta, Unio, and the freshwater pearl mussel Margaritifera margaritifera (cf. Brander, 1955, in Neves et al., 1989; Baumann and Everding 1986; Hochwald 1990; Zimmermann et al. 2000). This indirectly affects rare fish species that deposit their eggs in bivalves, such as the bitterling (Rhodeus amarus).

Disease transmission

Seven trematode, three nematode, two cestode, one acanthocephalan, one protozoan, and three acarine species were recovered from 171 O. zibethicus taken in Manitoba, Canada. The fluke Quinqueserialis quinqueserialis was the most abundant. found in 93% of animals examined and with up to 1856 worms per host. Young muskrats were parasitized shortly after weaning, with the most prevalent parasites being acquired first. Capillaria michiganensis and Hymenolepis sp. were significantly more prevalent in female muskrats than in males (McKenzie and Welch, 1979).

O. zibethicus serves as an intermediate host for the cestode Echinococcus multilocularis. Infection rates can be up to 28% in wild populations (Genovesi, 2006); other reports range from 0.1 % (Borgsteede et al., 2003) to 11.18% (Hanosset et al., 2008).

In a study in Washington State and Idaho, USA, Campylobacter jejuni was recovered from 47.5% of O. zibethicus faecal samples, and Giardia spp. were detected in 82.5%. These findings indicate that O. zibethicus may be of importance to the health both of humans and of domestic animals (Pacha et al., 1985; Bitto and Aldras, 2009). In recent years several waterborne outbreaks of human diarrhoeal disease have occurred in various rural and mountainous areas of the United States. Some of these have occurred among recreationists frequenting high mountain areas, while others have been associated with municipal water systems. Giardia duodenalis has been implicated as the causative agent in many of these outbreaks, but in some instances Campylobacter jejuni has been reported as the responsible agent.

Petri et al. (1997) found that O. zibethicus could be a source of contamination of surface waters with oocysts of Cryptosporidium.

It appears to be susceptible to plague through subcutaneous infection by blood-feeding parasites and from feeding on the organs of animals which have died of plague (Anon., 1940).

Large multilobular pseudocysts characteristic of Toxoplasma microti have been found in the brains of O. zibethicus (Karstad, 1963). The species can also harbour leptospires (the cause of Weil’s disease in humans), hantaviruses, Borrelia (where ticks are abundant; this organism causes Lyme disease), liver flukes, and Francisella tularensis (the cause of tularemia) (Steiner et al., 1992; Moll van Charante et al., 1998; Feldman, 2003).

Social Impact

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Human injuries and deaths are reported due to accidents when burrows collapse under tractors or other agricultural machinery.

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Highly mobile locally
  • Benefits from human association (i.e. it is a human commensal)
  • Fast growing
  • Has high reproductive potential
  • Gregarious
Impact outcomes
  • Altered trophic level
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Infrastructure damage
  • Modification of hydrology
  • Modification of natural benthic communities
  • Modification of nutrient regime
  • Modification of successional patterns
  • Negatively impacts agriculture
  • Negatively impacts human health
  • Negatively impacts animal health
  • Negatively impacts livelihoods
  • Negatively impacts aquaculture/fisheries
  • Reduced amenity values
Impact mechanisms
  • Pest and disease transmission
  • Herbivory/grazing/browsing
  • Predation
Likelihood of entry/control
  • Difficult/costly to control

Uses

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Economic value

Although O. zibethicus was introduced to many places as a fur animal, its economic value is currently almost nil because there is no demand for its fur.
 
Environmental services
 
The general opinion on the impact of O. zibethicus on its habitat is mixed, especially in northern Europe. Despite its negative effects, it is also regarded as a positive factor because it creates openings in dense vegetation stands and it prevents lakes from being overgrown by vegetation (Birnbaum, 2006).
 
The literature makes references to more than 60 vertebrates that use lodges or bank burrows built by O. zibethicus for shelter, nesting, getting above the water, or seeking food. These include turtles, waterfowl, terns, carnivores, rodents, and other species. None depend solely on O. zibethicus homes but their availability may limit some species (Kiviat, 1978).

Uses List

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General

  • Research model

Materials

  • Skins/leather/fur

Similarities to Other Species/Conditions

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The Coypu Myocastor coypus is also an invasive species in Europe. It was introduced sooner than O. zibethicus in most European countries but has disappeared from Scandinavia and, like O. zibethicus, was exterminated in the British Isles. A native of South America, it is less resistant to low temperatures, which constitutes a limit to its current expansion. However, climate change could benefit it. The biology and feeding habits of the two species are different enough for signs of their presence to be distinguished.

Prevention and Control

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Eradication

The Bern Convention on the Preservation of European Wild Plants and Animals and their Natural Habitats (Bern Convention Standing Committee, 1999) lists O. zibethicus in Recommendation No. 77 among those species which demonstrably pose a threat to biological diversity, and therefore recommends its extermination. Eradication is only possible on islands where there is no flow of individuals. The best example comes from the British Isles where the introduced animals were systematically exterminated. In continental situations, it is possible to eradicate animals on one site, but pioneer movements of young individuals can result in the return of the species if a high pressure of capture is not maintained.
 
Control
 
Slowing the rate of spread and controlling the population size in critical situations remain the only realistic ways in which this species can be controlled. Control methods include trapping, shooting, poisoning, disturbance, and exclusion (Kadlec et al., 2007). It is necessary to destroy more than 50% of individuals before the breeding period in order to cause a decline in numbers (Doude van Troostwijk, 1977). Research cited by Kadlec et al. (2007) found that numerous studies indicated that a population could remain sustainable with 50-90% of animals harvested every year. So, eradication is only possible with very high control pressure.
 
Physical/mechanical control
Trapping:
This is the most frequently used method of control. It can have an impact only with a very high pressure of trapping. It can be very efficient and catch large numbers of animals. For example, the annual muskrat catch in Finland usually varies between 200,000 and 300,000 individuals (Pankakoski, 1983). Research cited by Kadlec et al. (2007) found that on one site in Southern Ontario, Canada, trappers removed 400 muskrats from a 6 ha Typha wetland during a 2-week period in the autumn of 2003. However, due to high fecundity, populations can recover quickly. The most effective capturing devices are stove-pipe traps and Conibear®-type traps (not allowed in Europe under the Council Regulation 3254/91). Another well-adapted trap is the Stop-loss type. However this is sometimes described as being not selective enough and could trap birds such as the Moorhen Gallinula chroropus and Coot Fulica atra. Some traps work with baits, in particular carrots, celery or fruits. During the spring, some musk drops near the trap increase its attractiveness.
 
Shooting:
Shooting is possible at dawn and dusk when O. zibethicus is most active. However, it is not an efficient control method because only low numbers of animals can be killed this way.
 
Movement control
 
According to Burghause (1996), the "most successful, but also the most expensive" form of O. zibethicus indirect control is fortification of embankments. The banks of water bodies are protected against O. zibethicus by inserting a layer of plastic foil. These sections are additionally reinforced with a strong layer of large stones.
 
Exclusion from sites is possible using fences composed of galvanized wire mesh (5 cm x 5 cm) buried to a minimum depth of 0.30 m depth to prevent burrowing.
 
Biological control
 
The main predators of O. zibethicus, in particular (in Europe) the fox (Vulpes vulpes), the polecat (Mustela putorius) and the mink, could in theory exert a biological control effect (and in Poland the American mink, Mustela vison, appears to be an important factor in the decline of the muskrat population (Brzezinski et al., 2010)), but unfortunately these species are frequently more trapped than their preferred prey.
 
Chemical control
 
Chlorophacinone can be used to destroy O. zibethicus. In Belgium, the first studies were made by R. Moens starting in 1966 and led to the use of this chemical (research cited by Giban, 1974). The mortality obtained with a single ingestion is 100 percent when chlorophacinone baits are used up to a dosage of 0.005% of active material (rat dosage). Carrots and beet slices constitute well accepted baits, even during the vegetation season. Chlorophacinone seems not to affect carrion-feeding species and O. zibethicus does not seem to develop resistance to it (Giban 1974).
 
Zinc phosphide (63% concentrate) and anticoagulants are also used to control O. zibethicus. However, undesired impacts of toxicants on non-target species have been reported. Poison baits are usually placed on floating platforms to minimize risks to non-target species (DAISIE, 2009).
 
Chemical control may be forbidden in some European countries.

Gaps in Knowledge/Research Needs

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As eradication is not possible, it is urgently necessary to develop measures of O. zibethicus control, based on single site analysis. In some cases, O. zibethicus can play a positive role in some sites and it could be more detrimental than useful to try to eliminate too many animals. Studies of population dynamics and feeding habits are still necessary.

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25/09/09 Original text by:

Patrick Triplet, Syndicat Mixte Baie de Somme Place de l'Amiral Courbet, 80 1000 Abbeville, France

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