Aggressive, pugnacious, active both day and night, voraciously hungry and reputed to have a poisonous, paralysing bite. Conservation Officer, Simone Bullion, takes a look at this 'fearsome' beast and explains why we need to find out more about its way of life.

You could be forgiven for imagining that this animal is ferocious and best avoided. Britain's tiny, secretive water shrew leaves few signs and is under threat through habitat loss and pollution.
Just like other species of shrew, water shrew are insectivores, like our familiar hedgehog and mole. They are also able to hunt for food in water and will catch shrimps and caddis fly larvae as well as small frogs and fish. It is essential that they eat at least half their body weight every 24 hours otherwise they will starve. In fact they must keep up their frantic search for food all year round as they don't hibernate in winter. Their lives, therefore, are extremely hectic but short - they rarely survive a second winter.

Small enough to fit on a credit card, water shrew, like all shrews, have a long pointed nose, tiny eyes and ears. Their dense, velvety fur has a distinctive appearance being strongly two-tone, with a dark back and pale silvery underbelly. They even have fringes of hair on their feet and on the underside of their tail - an adaptation to an aquatic way of life helping them to swim and steer.

Water shrew are recorded throughout mainland Britain and a few offshore islands, but they aren't particularly numerous anywhere. Usually they inhabit the banks of clear, fast-flowing, unpolluted rivers and streams as well as ponds and drainage ditches. But they can also turn up some distance from water in woodland, hedgerows and grassland. In Suffolk there are very few records, although they have spread through most of the county, particularly around water.

Because they are rarely seen and don't leave specific field signs like other small mammals, they are difficult to study. All shrews make a high-pitched, squeaking sound which is often mistaken for birds or crickets. When one shrew meets another a twittering pandemonium breaks out and this strident sound, which is clearly audible, may be accompanied by chases and scuffles!

In recent years, water shrew has become progressively threatened by loss of habitat, particularly though disturbance and modification of pond and stream banks. Pollution of streams is also likely to be significant. However, because they are so under-recorded, it is very difficult to assess the extent of these effects. It is likely that Suffolk remains a significant area for water shrew because of the large number of streams, dykes and ponds.

In recognition of this, the water shrew has been named as a Suffolk Biodiversity Action Plan species. These plans help to set conservation targets and monitor change at a local level. Suffolk Wildlife Trust, in partnership with Suffolk Biological Records Centre, is collecting water shrew records which will improve our understanding of their local distribution. This will enable us to identify potential threats and help us encourage appropriate habitat management.

What can you do to help?
Water shrew will take up residence underneath corrugated iron which provides warmth and shelter. The sheets are best positioned on a grassy bank (with the landowner's permission) in sun and partial shade. This is an ideal way to record them as the sheet can be inspected several times during the summer and the animal is free to come and go as it chooses. All shrews benefit from protection under the Wildlife & Countryside Act (1981) which means a licence is needed if they are to be detained in a trap.

Why does the water shrew need help?
Water shrews are an elusive species that occur throughout Britain but nowhere are they common. They are difficult to survey and consequently few records exist to evaluate whether they are declining. However, the latest evidence suggests they may not be so rare as was first thought.

How do I recognise a water shrew?
- black fur on their back with a pale grey/white underside
- a small body about 11cm-17cm long from nose to tail
- frequently have white patches above the eyes and ear tips
- a fringe of silvery-white hairs along the tail and on the hind feet to increase propulsion when swimming.
- an elongated snout with sensitive, mobile whiskers to detect prey while swimming

Where do you find water shrews?
Water shrews live close to streams and rivers, watercress beds, ditches, pond edges, reedbeds and occasionally on the rocky seashore. However, they may be found in terrestrial habitats too, such as woodlands, grassland and hedgerows. They usually prefer well vegetated banks (which provides them with important cover from predators) near clear, unpolluted water.

Water shrews tend to live solitary lives but may also live in small groups of 4-6 individuals. They are known to disperse to distances of 160m. Population densities are typically low and even favoured habitats such as watercress beds, contain between 3-10 shrews per hectare.

What do they eat?
Unlike other small mammals, water shrews feed on aquatic crustaceans (e.g. shrimps) and insect larvae (caddis fly). They are expert swimmers and can dive up to 2m depth to forage for prey. However, before diving, they must leap to break the water surface and overcome their natural buoyancy. Terrestrial invertebrates (such as beetles, molluscs, spiders and worms) supplement the water shrews diet, together with the occasional small fish and amphibian. They do not hibernate during the winter and so must continue to forage for food both underwater and on land in order to stay alive.

How can you tell if there are water shrew's present?
Water shrews create extensive burrow systems using their feet and nose but will also re-use existing burrows. Entrance holes (usually 2cm in diameter) may occur both above and below the water level and are accompanied by established runways. Feeding sites and periodic middens (dung piles) can also be found nearby. Faecal remains (called scats) are approximately 7mm x 2mm and dark brown/black in colour. They have a crumbly texture and contain shiny fragments of snail shells, larvae cases and other remains.

What are the water shrews predators?
Water shrews are eaten by owls, kestrels, pike, stoats, weasels and mink but many carnivores find shrews distasteful and therefore tend to reject them.

Legal protection
Under the Wildlife and Countryside Act, 1981, it is illegal to capture or kill any species of shrew without a licence.

Threats to water shrews
Little is known about water shrews but the main threats are suspected to be:

- Habitat loss due to insensitive watercourse management and water flow alteration
- Fragmentation of riverside habitats which, in turn, isolates small groups of water shrew and increases the risk of local extinction
- Pollution of streams and rivers by harmful substances which may poison the shrews directly or reduce their food source
- Disturbance through increased human activity and the removal of vegetation cover

Best management practices and habitat improvement
Water shrews share similar habitat requirements to those of water voles and so their habitat can be managed in similar ways. In brief, these include:

- Sensitive management of vegetation, when banksides need to be cut, by removing alternate 50m sections (leaving an area of dense vegetation for cover).
- Increase the potential habitat area by providing ponds, ditches and buffer strips on adjacent land
- Re-profiling ditches to increase the availability of marginal vegetation (i.e. create a shelf along the bank).
- Fencing in riverbank vegetation so it grows back naturally.

Note: Where active maintenance and development is undertaken, it should be conducted outside the water shrew breeding season (which is April-September). One bank should be left untouched as a refuge and disturbance to the bank sides should be avoided if possible when de-silting. Any resulting spoil should be disposed of carefully.

Survey information

For more information
Penny Hemphill, Suffolk Wildlife Trust, Brooke House, Ashbocking, Ipswich, IP6 9JY
Tel 01473 890089 or email penny.hemphill@suffolkwildlifetrust.org