Life is tough for a pygmy shrew in Ireland

There was a corpse on the path in front of me. A very small corpse. 

A closer look revealed a short tail and a pointed face with tiny eyes. A pygmy shrew that had died quite recently for no obvious reason. Pygmy shrews are quite common in a variety of habitats in Ireland but they’re shy creatures that seldom venture far from cover so they’re not seen that often and, until you see them, it’s hard to realise how small they really are. On average an adult weighs 5 or 6 grams. In comparison an adult mouse, whether it’s a wood mouse or a house mouse, will be three to four times heavier.

This gives the pygmy shrew the uncontested title of smallest mammal in Ireland. It’s not, however, the smallest mammal in the world. That honour may belong to a bat that was discovered in 1973 in Thailand called Kitti’s hog-nosed bat, also known as the bumblebee bat because it’s the size of a large bee. Although it’s the smallest mammal by size the smallest by weight is the Etruscan shrew which averages 1.8 grams. They live in southern Europe and Asia and North Africa.

I looked at the little animal lying on my garden path and wondered if it had died of starvation. Because of their small size shrews have an extremely rapid metabolism. To survive they need to eat between one and a quarter and one and a half times their own body weight every day. This amounts to about 125 prey items in 24 hours. If they go more than about two hours without eating they starve. They do not hibernate and this metabolic demand means that they never sleep and seldom rest for more than a few seconds.

They are insectivores, which means they’re not remotely related to mice, which are rodents. A study of the diet of pygmy shrews in Ireland revealed that the commonest prey item was small to medium sized beetles. But other studies in Britain indicate that wood lice are a major component of their diet and it’s likely that Irish shrews eat them as well when they’re available.

They’re preyed on by birds — kestrels, buzzards, and owls — and cats kill a lot of them. They don’t dig burrows, though they will use ones made by other small mammals, and spend most of their time foraging in thick cover — long grass, heather or hedge bottoms.

It’s a stressful existence, continually hunting for food and being continually hunted yourself. But the stress increased in 2007 when biologists discovered that the greater white-toothed shrew had become established in Co Tipperary and was spreading to surrounding counties. It appears they were accidentally introduced from the Netherlands in nursery shrubs. This shrew has similar habitat and diet preferences to the pygmy shrew but is three times the size and preliminary research suggests it may be out-competing it.


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