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Rescuing Ratty
Water Shrews
Water Voles
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Water Shrews
Location: Northumberland
 Water Shrew Information
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 we would like to confirm this theory.
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, only 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 shrew’s 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 license.
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 other riparian species 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.
How do I look for Water Shrews?
The biggest problem with conserving the water shrew is the lack of existing information about its distribution, population status and habitat preferences. We need more data so that accurate recommendations can be based on firm evidence.
There are several simple methods to conduct water shrew surveys and they can be carried out at any time of the year (though they are most successful in the summer and autumn). They are as follows.
Refugia without bait
Sheets of corrugated iron or bitumen roofing felt (ideally 0.5m x 1.5m) can be placed near riverbanks and stream edges. The warm, sheltered conditions generated by the sheets attract inquisitive small mammals who then enter underneath. Once the refugia has been left in a partially shaded place for 2 weeks (so the grass has died back) the sheeting can be lifted to expose any creatures present. It’s generally best to conduct the survey in twos so that one person can lift the refugia while the other observes the rapidly escaping occupants! The sheets can be inspected several times during the summer/autumn but its worth noting that the warm conditions under the sheets may also attract reptiles, including adders, so beware!
Refugia with bait
The procedure is essentially the same as above but includes sliding a white plastic lid or sheet with a handful of blowfly pupae, under each refugium. The water shrews can then eat the bait and, hopefully, will produce scats (which will be clearly visible against the white of the plastic). The scats must be recovered from the refugia, dried in fresh air and stored in paper envelopes.
The faeces can then be analysed for remains of aquatic prey (a sure sign of water shrews). Any scat samples sent to us at SWT for analysis will be gratefully received, or if you like you can analyse the scats yourself.
Bait tubes
Bait tubes are simply lengths of white plastic tubing (approximately 4cm in diameter and 20cm long) with bait stored inside. The basic principle is like that of refugia with bait. However, one end of the pipe is covered with muslin or nylon netting (secured in place with a rubber band). The bait is placed towards the covered end of the tube and the open end should be flush with the ground to allow small mammals to go in easily. Bait tubes should be laid flat amongst the bank vegetation using small wire hoops pushed in the ground. The piping can then be retrieved (after 2 weeks) and the scats analysed.
Whichever method is used, it is important to mark on a map where the refugia or bait tubes were placed and the type of vegetation it was located in (woodlands, grassland, scrub). Additional notes on: the speed of the water flow (fast, slow, static): the substrate type (rocks, gravel, mud): the adjacent land use (pasture, arable, woodland, fen): and the management would all be invaluable in helping us to understand the needs of water shrew.
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