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Pygmy Shrew

Pygmy Shrew by Terry Coult

The Pygmy Shrew is Britain’s smallest mammal weighing only 2.3-5 g and measuring 40-55 mm head and body with a tail 30-46 mm. It is brown in colour grading to a paler underside. The tail is hairier and appears thicker than that of the Common Shrew Sorex araneus and at about two thirds of the head and body length it is relatively longer. It may be of some help in separating the two species to remember that while the Pygmy Shrew may reach five grams in weight, this is the weight at which the Common Shrew leaves the nest.

The Pygmy Shrew is distributed over mainland Britain and many of the islands, in a wide range of habitats wherever there is a litter layer to conceal it and through which it can burrow. They also use the burrows of other animals, but it is not as subterranean as the Common Shrew. It is generally less numerous in all habitats than the Common Shrew except on moorland and blanket bogs. They seem to fare better than the Common Shrew in wet and dry habitats. Millais (1906) records a Pygmy Shrew that was brought in by a cat to the observatory on top of Ben Nevis.

Pygmy Shrews are difficult to catch using Longworth traps because of their light weight. It is difficult to set the trap to respond to such weights and not trip at other slight disturbances. To illustrate this, they were a mere 4% of the total number of small mammals caught in Longworth traps in the North East by Veronica Carnell, the same percentage as Water Shrew Neomy fodiens (V. Carnell, pers. comm., 2012), though the latter is almost certainly a much less common and more habitat-restricted species. Where they are successfully trapped, they form about 4% of small mammal captures in deciduous woodland, 5-38% in grassland, and in pitfall traps in northern England on moorland and blanket bog have formed 80-90% of the catch (Churchfield and Searle in Harris and Yalden, 2008). Anecdotally they are often drowned in pitfall traps set for invertebrates though unfortunately this by-catch is often not recorded. Their presence can often be deduced by finding droppings in unsprung traps.

Though smaller, they have a larger home range (500-1800 metres2) than the Common Shrew’s (900 metres2). The breeding season extends from April to October and litters of one to nine (normally four to six) are born in similar conditions to the Common Shrew. The young are around 0.25 g at birth and become independent at around 2.5 g. They over-winter as immature animals and die before the following winter.

Their food preferences are similar to Common Shrew but probably because of their size they choose smaller, less well-armoured prey and take more from the surface rather than burrowing in the soil. This is possibly the ecological separation that enables both Pygmy and Common Shrew to share the range. That they can do so without conflict is interesting. Harrison Matthews (2009) suggests that the Pygmy Shrew is fast enough to respond to approaching Common Shrews so that though it knows the Common Shrew is present the Common Shrew is not aware of the smaller animal. This however discounts the sensitivity of their noses and the presence of the scent glands. That the smaller animal would appear on the menu of the larger if caught is probable unless they find them unpalatable, as cats apparently do. Veronica Carnell reports catching both species in the same trap and that both were uninjured (V. Carnell, pers. comm., 2012), though in this situation easier sources of food (bait) would be present.

MARS Pygmy Shrew

Within the North East it is referred to in The Victoria History of the County of Durham as follows: “Only one record a specimen in Newcastle Museum taken by W. Backhouse at St. John’s Wolsingham but probably not as scarce as lack of records suggests” (Page, 1905). In Longstaffe’s History of Darlington (1854) it is not mentioned though the other two shrew species are.

Modern records, though less numerous than for Common Shrew, show a similarly widespread distribution. However it has only been recorded in 28 10 km squares in the North East, post-2000, which is not a great improvement on the 21 10 km squares from which it was recorded in the 1993 Atlas of Mammals in Britain (Arnold, 1993). This is probably an indication of observer coverage and, in terms of the comparison between the coverage of records and the species’ likely distribution, it is probably the most under-recorded mammal in the North East.

References

Written by Don Griss (last updated Nov 12)