Least Shrew

Cryptotis parva (Say)

 

 

Description:   Least shrews are the smallest mammal in Kansas, and not much larger than the smallest mammal in the world. This shrew can be distinguished from other Kansas shrews by: 1) general dorsal color brownish gray in summer, darker brown in winter with a gray belly in both seasons (young are a dark slaty-gray), 2) long, pointed nose or muzzle (in comparison to its body size the muzzle is longer than that of the short-tailed shrew), 3) eyes that are smaller than other species of small Kansas mammals, 4) relatively small, delicate legs and feet, 5) uniformly soft hair, which in microscopic examination exhibits a "hinge" or "bend" segment, and 6) reddish-black tipped teeth, 30 in number (two less than in the Hayden's and short-tailed shrews). They can be distinguished from the short-tailed shrew by their smaller size, and from Hayden's shrew by their much shorter tails.

Size:   Adults attain the following dimensions: total length 71-86 mm; tail 15-18 mm; hind foot 10-11 mm; ear 9-11 mm; weight 4-6 grams.

Range and Habitat:   The distribution of the least shrew is statewide, but because the edge of the range of this species is in western Kansas some areas there may not be inhabited. This shrew is more tolerant of drier areas than southern short-tailed shrews. They are found in most of the terrestrial plant communities in Kansas, preferring dense grasslands, successional growths around ponds and lakes, and deciduous forests. Least shrews use runways of prairie voles, cotton rats, and other small mammals, but will make and use their own runways and tunnels on the surface or in soft soils.

Reproduction:   Least shrews breed two or three times a year, between early spring and late autumn. Gestation is from 21-23 days when two to seven (usually four to six) naked young are born with eyes and ears closed by skin. After one week they are furred; at two weeks of age the eyes open; and shortly thereafter they follow their mother by grasping her tail or the tail of a littermate in their teeth. At 20-22 days they are weaned and can lead independent lives. At one month they are full-grown and at three to four months capable of breeding, although this is usually deferred until the following spring. Ordinarily the female rears the young alone, but on many occasions an adult male and female are associated with the young. The nest, 100 to 200 mm in diameter, is concealed under a log, stump, flat rock in a shallow ground cavity, or more rarely in a burrow. It consists of dried leaves, grasses and other vegetable fibers. Larger nests are used in winter and may contain a dozen or more shrews-to this extent they are gregarious.

Habits:   Least shrews have an unusually high rate of metabolism (about 10 cm3 oxygen per gram body weight per hour). As a result of the high energy loss, the need for food is almost constant. In 24 hours it eats 60-100 percent of its weight. The demand for energy is so great that if it is without food on a cold day it will starve in a short time. For this reason, least shrews are difficult to keep in captivity and will frequently die from lack of food. The high energy requirement is related to the difficulty of retaining body heat with a relatively large skin area to small body mass. When awake or active least shrews appear nervous, but when inactive sleep soundly. The home range is reported to be about 0.3 hectares.

Food:   Food of least shrews is principally insects, earthworms, snails, and carrion. When normal food is scarce they may eat seeds and fruit. Emergency supplies of food are cached.

Remarks:   Although it is seldom seen by humans except when brought in dead by a cat or seen running across the road at night, this shrew is generally common. Like southern short-tailed shrews, least shrews are eaten by snakes, hawks, and owls. Carnivorous mammals capture and kill these shrews, but rarely eat them because of the specialized skin glands that are distasteful to these carnivores. The principal gland is the flank gland, which is better developed in males than females after sexual maturity. Least shrews have a maximum lifespan of 16 to 18 months.


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