Nine species of shrews live in Colorado, but most are seldom seen because they live under the vegetation on the forest floor. They are among the least known of our native mammals.
Most shrews are tiny. The pygmy shrew – less than four inches long and weighing in at barely a tenth of an ounce – is tied with the least shrew of Europe and the bumblebee bat of Thailand for the record of being the smallest mammal. Our largest Coloradan shrews (the water shrew and the southern short-tailed shrew) are giants by comparison, almost mouse-sized, weighing about three-quarters of an ounce. Other kinds are in between.
Shrews have tiny eyes, a pointed snout (the German word for shrew is Spitzmaus – "sharp mouse") and tiny ears hidden in velvety, dense fur. Most shrews are brown, but the water shrew is nearly black with a silvery white belly, and the desert shrew is gray. Shrews have a strong odor, and carnivores other than owls tend not to bother them much. House cats kill them but seldom eat them. Perhaps you are most likely to see a shrew if your cat catches one and leaves it on the porch as a "gift." They are extremely active, with heart rates of 600-1,200 or more beats per minute. Shrews live in a hurry. A year-old shrew is a very old shrew.
Habitat: Most shrews live in moist habitats. The desert shrew seeks humidity in arid areas, such as wood rat dens.
Diet: Shrews eat mostly insects – adults, larvae, pupae, eggs. Shrews can kill mice twice their size, however, and they also eat carrion. In fact, they eat meat in any form, but little vegetation.
Reproduction: Shrews breed during the warmer months of the year. Gestation takes about three weeks. Shrews have been observed performing what might be called a shrew conga line. A family of mother and young will fall into line one behind the other, the first young grasping the fur around the mother’s tail, the next grabbing the rear of the first baby and on down the line. The line then snakes its way through the undergrowth. By mimicking the movement of a snake, this may be a protective behavior that gives the family of tiny shrews some safety from predators.
By David M. Armstrong
Department of Ecology & Evolutionary Biology
Environmental Studies Program, University Museum of Natural History
University of Colorado-Bouldermausmann@aol.com