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Common Shrew

Common Shrew by Joan Holding

The Common Shrew Sorex Araneus is believed to be the second commonest mammal in Great Britain, with an estimated population of around 41.7 million. It is small and brown with a contrast between the upper and undersides. The flanks are a different shade to the back giving it a tricoloured appearance. They sometimes have white ear tufts, similar to Water Shrews Neomys fodiens: Veronica Carnell caught one such individual in Gosforth Park, Newcastle upon Tyne. The head and body are 48-80 mm and the tail 24-44 mm. Weight is from 5-14 g. The tail is a little over half the length of the head and body (cf. Pygmy Shrew Sorex minutus) and does not have a distinctive fringe of hair along the underside as does the darker coloured Water Shrew.

It is found in a wide variety of habitats in which there is a litter layer where it can form covered runs to escape observation. It also uses the burrows and runs of other small mammals such as mice and voles and is thus often difficult to detect. Most common in grasslands, it is quick to colonise field borders and other areas of recovering vegetation. In Britain it is found to elevations of around 1,000 metres in the uplands, most frequently in stable scree but occasionally in heather. Population density varies from as low as five to as high as 90 per hectare, with variation depending on vegetation type and season. A line of eight Longworth traps set at roughly five metres apart along the base of a wall in Blanchland in the North Pennines, in March 2012, caught Common Shrews in five traps on the same night, the remaining three traps catching Bank Voles Myodes glareolus (I. Bond, pers. comm., 2012).

During the summer they can often be heard squeaking in vegetation. This is because they live solitary lives and when they meet may fight or become involved in a squeaking “duel”. The young are born between May and September in litters of three to nine in a large concealed nest of grass and leaves. In the latter stages of rearing the young the female may need to eat up to 120% of her body weight per day (Churchfield, 1986). Shrews are short-lived, normally over-wintering as immatures which are smaller (seven g) and greyer than the adults. They moult in autumn and spring. Moulting individuals can easily be recognised as the autumn moult starts at the tail and moves along the body to the head, giving the animal a peculiar parti-coloured appearance. In the spring the moult goes in the reverse direction.

Shrews are active hunters, using scent, touch and hearing to locate their prey. Their eyes are very small and probably not very efficient. Prey consists of insects, spiders, crustaceans, worms, etc. Its high metabolic rate means it must eat about 70% of its own body weight per day (Churchfield, 1986). This rate of activity causes tooth wear, which is one of the causes of death (Harris and Yalden, 2008).

Common Shrew, Harwood Forest © John Steel

Numbers are highest in summer but fall rapidly during October and November. There are two reasons for this fall, firstly the death after breeding of the adults and secondly the high mortality of inexperienced juveniles establishing winter ranges. They are preyed on by a wide range of birds, but while mammals may kill them some, such as cats, will not eat them, being put off by the scent glands on the flanks. Shrews rank as the second or third preference as food for owls, behind rodents (mice and voles). They may be taken when rodent densities are low. Out of 1,307 prey items identified from a total of 671 Long-eared Owl Asio otus pellets from Urlay Nook, only one was from Common Shrew, less than 0.1% (A. Love, pers. comm. to Alistair McLee, 2004). However this can vary depending on other factors such as the species of owl and the type of habitat that they hunt over. Barn Owls Tyto alba that hunt over closely cropped and tussocky grassland will typically take a higher proportion of shrews (Taylor, 1994). For example, of 39 prey remains recovered from Barn Owl pellets from a roost near Greatham surrounded mainly by pasture, six (15%) were from shrews; and from young woodland plantation near Darlington, around one quarter of the 33 prey remains were Common Shrew (I. Bond, pers. comm., 2012).

Their comparative abundance and high death rate cause them to be frequently found dead on footpaths and other open places, although this can be because they have been abandoned by cats or other predators. It was however at one time believed to be because they could not cross a human track. They were also thought to be so sensitive that they died of shock. They are however much more robust and can develop a trap habit if caught in Longworth traps, returning for a further feed of blow fly pupa in spite of the handling procedures. It should be noted that it is now illegal to trap shrews without a licence.

Though not normally injurious to man or his animals, shrews were once subject to a particular form of cruelty because of the superstitious belief that they were venomous and caused damage to animals by walking over them, to the extent that the animals could lose the use of a limb. To cure this, a hole was bored in an Ash tree and a live shrew was placed in it. The hole was then plugged and when the shrew had died of hunger (which wouldn’t take very long) the so called Shrew Ash became imbued with the power to cure these beasts. All that was needed was to draw a twig or branch from the tree several times across the back of the sick animal. This belief was widespread and Shrew Ashes, which kept their power until they died, were found across the country (Brockie, 1886).

MARS Common Shrew

While widely distributed, our map shows a preponderance of records in the eastern lowlands but this is probably as much an effect of observer distribution as that of the shrews. However the large areas of heather moorland in the west, where population densities are low, might have some effect. They can certainly be common: of all the small mammals caught in Longworth traps in the North East by Veronica Carnell, over the ten years to 2012, almost one quarter were Common Shrews (V. Carnell, pers. comm., 2012). Historically within the North East small mammals are not widely mentioned but The Victoria History of the County of Durham (Page, 1905) refers to the Common Shrew as abundant, a situation that has almost certainly not changed despite the lack of records.

 

References

Written by Don Griss (last updated Nov 12)