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Eurasian Water Vole

Arvicola amphibius

French: Grand Campagnol / German: Ostschermaus / Spanish: Rata de agua euroasiatica

Other common names: European Water Vole, Water Vole

Taxonomy. Mus amphibius Linnaeus, 1758, England.

Arvicola terrestris and A. scherman are synonyms. In the last decade, species of Arvicola, other than A. sapidus, were split into large aquatic ( amphibius) and small fossorial (scherman) species. Phylogenetic reconstructions showed, however, that fossorial and aquatic voles do not segregate into discrete evolutionary lineages hence the “morphotype does not make a species in water voles.” Taxonomic division adopted here is mainly based on genetic lineages retrieved from molecular markers. Arvicola amphibius is a polytypic species, and up to 16 subspecies have been distinguished in Russia alone. Due to disconnected patterns of morphological and genetic variation, there is little consensus on subspecific taxonomy. Polytypic, but number, diagnoses, and ranges of subspecies require review.

Distribution. Great Britain, C Europe, and Scandinavia, and across E Europe, Anatolia, Caucasus, NW Iran, and Kazakhstan to Siberia (E to Lake Baikal and Lena River), extreme N Mongolia (Mongolian Altai and Hovsgol Mts), and NE China (N Xinjiang); also present on many islands and islets in Baltic and North seas.

Descriptive notes. Head-body 120-230 mm, tail 58-139 mm; weight 80-320 g. Dimensions are highly variable, and aquatic forms are always bigger. Ranges for the two morphotypes in south-eastern Europe are as follows: head-body 165-191 mm, tail 96-122 mm; weight 134-200 g (aquatic morphotype) and head-body 130-175 mm,tail 58-102 mm; weight 58-172 g (fossorial morphotype). Male Eurasian Water Voles are larger than females. In England, where it attains maximum dimensions, head-body length and weight of males average at 188-4 mm and 219 g, respectively, while corresponding values of females are 180-9 mm and 196 g. The Eurasian Water Vole is large and robust, with heavy head, powerful limbs, and moderately long tail. Tail is relatively longer in aquatic Arvicola (48-82% of headbody) than in fossorial individuals (40-59%). Aquatic morphotype has more developed plantar and palmar pads. Ears hardly overtop fur, and eyes are small and protuberant. Females have two pairs of each, pectoral and the inguinal nipples (eight nipples in total). Fur consists of long and glossy guard hairs and woolly underfur, but guard hair is shorter and softer in fossorial morphotype. Most Eurasian Water Voles have brown back, gray belly, and indistinct demarcation along flanks. Ventral side is washed buff in many populations. Some local populations (e.g. Russia, Great Britain, and western Hungary) are entirely black, and others contain significant proportions of piebald individuals. Different color variants can co-occur in the same population or geographical race. In Armenia, most individuals (919%) were gray-brown, and remaining were gray, brown, or rusty. Proportion of color variants can vary between seasons and among years. Tail and paws are blackish brown. Skull is heavy and well ridged, with expanded zygomatic arches and relatively short braincase. Supratemporal ridges converge and form distinct sagittal crest in adults. Occiput is nearly vertically truncated, and upper incisors are orthodont in aquatic forms. Occiput of the fossorial form is inclined, and incisors are protruding (proodont) and less concealed by lips. Many populations show intermediate characteristics. Molars are robust and hypsodont. M’ and M, have simple patterns; former has short posterior cup, and latter has three closed and alternating dental triangles.

Habitat. Spatial distribution and habitat use differs between the two morphotypes at various scales. Most of the distribution of the Eurasian Water Vole is occupied by aquatic morphotype that lives from lowlands to high into the mountains. Fossorial morphotype is mainly associated with mountainous landscapes. Elevational range is from the sea level to 3210 m. Aquatic morphotype typically stays within 2 m of water’s edge in marshes, around ponds and lakes, and along ditches, streams, and rivers. Water has to be still or with a current less than 0-5 m/s and must be present throughout the year. Steep loamy or sandy banks enable digging, and dense vegetation provides grass for feeding, plant material for nesting, and cover from avian predators. Fossorial colonies are able to occupy larger areas of continuous habitat (e.g. pastures, clearings in forests, arable fields, and orchards). Some populations in Germany, Macedonia, and Russia seasonally migrate between wet and dry habitats.

Food and Feeding. Diet predominantly consists of green plants, tubers, and rhizomes. In Belarus, 92 different species of plants are eaten compared to 227 species in Great Britain. Daily intake is equivalent to ¢.80% of body mass. Diets contain common reeds ( Phragmites australis), floating sweet-grass ( Glyceria fluitans), red canarygrass ( Phalaris arundinacea), velvetgrass ( Holcus lanatus), and purple moor-grass ( Molinia caerulea), all Poaceae; braodlef cattail (1ypha latifolia, Typhaceae); common rush ( Juncus effusus, Juncaceae); western doc ( Rumex aquaticus, Polygonaceae); common comfrey ( Symphytum officinale, Boraginaceae); sedges ( Carex, Cyperaceae); nettles (Unrtica dioica, Urticaceae); dead nettles ( Lamium album, Lamiaceae); and meadow sweet ( Filipendula ulmaria) and tormentil ( Potentilla erecta), both Rosaceae . Carrot and potato tubers are eaten in gardens, and bark and roots are damaged in orchards. Insects, mollusks, crabs, and fish are rarely eaten. Piles of uneaten grass, sedges, and reeds are commonly found on runways. Clips of vegetation are typically c¢.10 cm long. Food is stored underground. Caches in a single burrow system can contain 4-5 kg of food, and stores of up to 35 kg were reported from the eastern edge of the distribution along the Lena River. Eurasian Water Volessit on hindfeet while feeding and manipulate food items with front paws.

Breeding. Breeding season of the Eurasian Water Vole is in March—-September in Central Europe and May—-August in western Siberia. Females are polyestrous, with postpartum estrus. Estrus can be suppressed during lactation. Mating system is promiscuous, and more than 50% of litters can be sired by 2-3 males. Large males father proportionally more offspring but cannot monopolize access to females. Gestation last 20-30 days, and females have 1-5 litters/season (mean c.3), with 1-11 young (usually 4-6). Young are born naked, with eyes closed, and weigh 3-5-5-7 g. Females lactate for 22 days, after which young leave nests. Eurasian Water Voles rarely mature in their first year. Although they can live up to three years, only a few survive a second winter. Longest recorded survival in captivity was 955 days.

Activity patterns. Eurasian Water Voles are active day and night. They swim well, and air trapped in dense fur provides additional insulation in water. Out of water, they move around by walking and running on the ground’s surface or through underground tunnels. Aboveground, they use 4-9 cm broad runways concealed by dense vegetation. They dislike crossing open spaces, and the aquatic morphotype stays underground when out of the water. Burrows are of two types: a simple tunnel ending in a chamber or a system of branching tunnels with multiple entrances and several chambers, including nest and 1-2 caches. Those dug into banks extend up to 1-5 m deep in Western Europe and up to 2:3 m in European Russia. In Russia, each burrow has 1-3 exits, and tunnels (4-5 m in length) expand over 2-5 m®. Cache is 30-50 cm beyond entrance, and nest chamber (20-22 cm in diameter) is located deeper. Burrows are more extensive and elaborated in fossorial populations. In Russia, total length of tunnels is ¢.24 m, and they expand over 50 m*. About 4 m of tunnels are used as caches. Eurasian Water Voles loosen soil with incisors and push it behind their bodies with foreand hindlimbs. Excavated soil is transported to the surface by hindfeet. Fossorial individuals deposit soil in heaps that seal entrances to burrows. Nests are woven from grass and lined with finely shredded plant material. When water levels are high, nests are constructed among vegetation just above the water’s surface.

Movements, Home range and Social organization. Home ranges of aquatic form of the Eurasian Water Vole are linear. Means for breeding individuals in north-eastern Scotland are 48-212 m for males and 25-47 m for females. Home ranges are larger for males, adults, and during breeding season. Males have overlapping and non-territorial home ranges, but females normally defend home ranges. Home ranges of females can overlap and remain undefended at high densities. Dispersal is frequent and extensive and is achieved by swimming or moving overland. Females disperse farther than males. Eurasian Water Voles communicate with series of short (0-1 seconds) and low-frequency (2:5—4-4 kHz) calls and by depositing chemical clues in urine and feces and scent marking using flank glands. Home ranges are marked by latrines. During aggressive encounters, individuals chatter teeth, scratch flanks, and beat tails. Long guard hairs are erect on excited individuals.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Eurasian Water Vole has a wide distribution, close to 15,000,000 km?, and stable overall population trend. Severe population decline is reported from UK and the Netherlands. In UK, decline was estimated at 94% in the 1990s. Eurasian Water Voles vanished from whole catchments and many islands, and numbers at occupied sites also declined.

Bibliography. Gromov & Erbajeva (1995), Krystufek, Koren et al. (2015), Panteleyev (2001), Popov (1960), Reichstein (1982b), Woodroffe et al. (2008).