The North American least shrew (Cryptotis parva) is one of the smallest mammals, growing to be only up to 3 inches long. It has a long pointed snout and a tail never more than twice the length of its hind foot. The dense fur coat is either grayish-brown or reddish-brown with a white belly. Its fur becomes lighter in the summer and darker in the winter. Although similar in appearance to several species of rodents, all shrews are members of the order Eulipotyphla and should not be mistaken for a member of the order Rodentia. The North American least shrew's eyes are small and its ears are completely concealed within its short fur, giving it very poor eyesight and hearing.
Distribution
It is found from the grasslands of southern Canada through the eastern and central United States and Mexico. In Canada, only a small population of this animal has been found at Long Point in Ontario.
The North American least shrew mostly dwells in mesic grasslands, marshes, and meadows. Most shrews prefer these wet habitats, but the least shrew will also inhabit dry upland regions. This species can be found in meadows, fields, and weedy areas, where the vegetation attracts its insect diet.
The North American least shrew makes its home in burrows or shallow runways under flat stones or fallen logs. Its burrows are about 2.5 cm in diameter, from 25 cm to 1.5 m long, and seldom more than 20 cm below the ground. Most shrews are aggressive towards each other, but this species is a social creature and often cooperates in digging its burrows and often sleeps with other shrews. From 2 to 31 of these shrews will live together at a time, although it is more common to find them together in the winter months to keep warm. It will line its burrows with leaves and grass in nests for the purpose of rearing offspring. The breeding season extends from early March to late November. Females produce two or more litters each season. Each litter will consist of about three to six young, each one weighing about 0.3 g, which grow quickly and will be adult size in about one month. Litters are born 21–23 days after copulation. When first born, young are deaf, blind, and hairless. At 14 days old, they will open their eyes and have fur. By day 21, they will weigh 4-5 g and weaning will begin. The North American least shrew rarely lives more than a year. Its natural predators are owls, hawks, the red fox, the raccoon, skunks, and snakes.
The primitive features of Cryptotis parva suggest its ancient origins. The zygomatic arches are missing in the skull, which are present in most mammals even of that size, such as rodents. The mandible also has a more primitive structure with a double articulating surface. The cerebral hemisphere is relatively small, which is necessary in manipulative abilities. However, the olfactory lobes are well developed, revealing the significance of the ability to smell in the shrew's survival. The reproductive and urinary systems are joined in one external opening, called the cloaca, which is a primitive character not found in higher mammals. Another trait uncommon in mammals is the testes are found inside the abdominal cavity.
Threats
The North American least shrew is listed as endangered in Connecticut and in Pennsylvania. The greatest threat to it is the development of coastal habitat, particularly dunes and marshes.
References
- The Mammals of Texas Revised Edition by David J. Schmidly