Northern Short-tailed Shrew
This fall I made the acquaintance of a mammal whose reputation proceeded it. What mammal eats up to three times its own weight in food? Has a poisonous bite? Tastes so bad other mammals won't eat it? Lives in pairs? And, if all of that was not enough actually hoards its food in fall in winter?
You probably have never seen one alive even though there may be between 5 and thirty of them living in a single hectare. The eating habits of this mammal should suggest to that it is a small mammal, likely an insectivore. The smaller a warm-blooded animal is the greater the area of its skin relative to its body mass. This animal is about the size of your thumb. Even though it is well furred it loses heat far more rapidly than you do so it must continually replenish its energy supply by eating. (An elephant, by the way eats far less food per day on a kilogram per kilogram basis than you do.)
The northern short-tailed shrew is an amazing animal. It is indeed an insectivore but it includes far more vertebrate animals in its diet than do other shrews, moles and other insect eating predators. It will eat young mice, voles and even nestling birds knocked out of their nest. Its bite is mildly poisonous (but not to you) and paralyzes prey up to the size of the shrew.
However, it is also an omnivore and not above visiting bird feeders to feast on fallen seeds and suet. Protein is protein. It was by our feeders that we first noticed the shrew. At first we thought it was a meadow vole but it was a silvery colour and voles are usually brown. It seems that we were seeing one in its fall/winter coat. The speed with which it moved impressed me but some of its moves were so fast it appeared to be in two places at once. It was then that we realized that we had a pair of them. While they are polygamous males and females sharing a territory is not that uncommon.
Of course all of this feeding is converted to energy both stored and used. Other animals you would think would find them easy prey. Mammalian predators such as red fox, coyotes and even squirrels find this vole too smelly and not at all to their taste. they may kill one from time to time but are not know to eat them. Owls and hawks are far less discerning and do prey upon them. A very high number of shrews do not survive their first year. Winter temperatures kill large numbers as they cannot get enough food to maintain their body weight.
The shrew responds to this pressure by producing lots of babies. They will have two to (rarely) three litters of between five and seven young per year. The young of the first litter may even breed during the fall of that year.
So why are they not seen more often? They spend a good deal of their time underground or under leaf litter. Their preferred habitats are moist and provide ample leaf litter. They can be found in grasslands, old fields, fencerows, marshy areas, deciduous and coniferous forests, and household gardens.
Especially if there are bird feeders there.
Note: A version of this article first appeared in Bob Izumi's Real Fishing Magazine in
Dave's column At the Water's Edge. It is used with the permission of editor.
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