Water Vole

Distribution

The water vole is found throughout mainland Britain, as well as Europe and Asia as far as eastern Siberia.
The 1996-98 survey has indicated a 94% population decline. When breeding females defend a home range that does not overlap with other females. Males however may overlap with other males as well as the female ranges. Densities can vary up to 114/km depending on the time of year. In Europe 4-8 year population cycles are exhibited.

Body

Water voles are large for a vole.
Males weigh 240-330g.
Females weigh 225-310g.
Compared to a rat they have:
blunter noses,
small sensitive ears,
a shorter lightly haired tail,
bright orange upper incisors
and rich brown fur.
Like other aquatic rodents they have dense fur that traps air for insulation as well as the longer guard hairs.
They moult in autumn and spring.

Field Signs

In the field the well-established runs in their home ranges are notable along with conspicuous latrines. At these are deposited the cylindrical, blunt droppings that are 8-12mm long by 4-5mm wide and consist of putty-like plant remains, but are often stamped on by the vole. Scent marking is achieved at latrines using scent glands on the flanks that are mature in voles as young as 3 weeks.

Feeding stations consist of short grazed vegetation with incisor marks and neat piles of grass or reed that are created as the vole leaves the less succulent parts. Also evident are the burrows and bolt holes that occur above, below and at the water line. These holes are 4-8cm across and wider than they are high. The existence of core and peripheral sites has been noted, with the latter only being used at certain times of the year, but these do not contain latrines.

Due to lower activity rates, field signs are often much reduced in winter.

Habitat

Sites with breeding voles have been found to have banks steeper than 35 degrees which enables the construction of the extensive burrow networks. These networks also allow for water level changes where lower burrows may become flooded. Also a high proportion of grass which is used as a nesting material is preferred. Better vegetation cover is also a more effective screen from predators.

Water vole prefer slow moving watercourses, ditches and ponds with relatively steep earth banks that are not regularly submerged during flooding. Also if there is sufficient tussocky vegetation for dry nesting sites then wetlands and water meadows make good habitat. Banks preferably have continuous dense stand of luxuriant grasses, reeds and sedges for cover and food.

Feeding

Water voles have been found to eat up to 227 different food plants. In summer these often include grasses, sedges, common reed and river crowfoot, but in winter tree bark, bulbs, roots and rhizomes are eaten. Their feeding adaptability also includes some tree climbing up to a height of several meters if the need arises. Fruit is eaten and apples are a good at tempting voles out for observation. Having large incisors allows them to eat coarser foodstuffs than other rodents. When eating they typically sit back on their haunches and use their forepaws.

Breeding

There can be up to 5 litters of 3-7 young between April and September following a 20-22 day gestation. Then follows a 14-day lactation. Few reproduce in the year of their birth although young born before July mature later that year.

65% of young die before maturity, of the survivors many do not make it through two winters and to survive three is rare.

Threats

Mink predation is a serious problem as they are able to hunt both in the water, on land and in the burrows. Rodenticides and herbicides pollute watercourses and impact populations. Habitat can be degraded through disturbance, dredging, grazed banks and bank reinforcement with metal pilings. Also developing flood plains can cause rivers levels to rise higher and for longer, which can flood them out.