Least shrews, Cryptotis parva, occur in greatest densities in the eastern United States. Their geographical range extends from Florida to New York and reaches as far west as Texas and South Dakota. Least shrews also occur in Central America from northern Mexico to Costa Rica and into Panama.

Biogeographic Regions: nearctic (Native ); neotropical (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Throughout much of eastern U.S. north (at least formerly) to extreme southeastern Canada (Hutterer, in Wilson and Reeder 1993), southern New York and southern Connecticut, southern Michigan (Evers 1992), and South Dakota; also south through Mexico (south to Chiapas, west to Nayarit) (Hutterer, in Wilson and Reeder 2005). Northern limit in eastern part of range may have contracted somewhat. Distribution expanded westward in the western Great Plains over the past few decades in response to the creation of relatively stable mesic habitat associated with increased irrigation and a simultaneous trend toward more mesic climate (Hafner and Shuster 1996). However, some western populations apparently represent relicts of late Wisconsinan and altithermal periods (Hafner and Shuster 1996).

Least shrews have dense, short hair, which is dark brown to reddish brown on the dorsal side during the winter. During the summer, fur becomes grayish brown in color. They have a bicolored tail, with a darker brown on top and a lighter underside. Least shrews measure 70 to 92 mm in length and usually weigh between 3 and 6 g. Members of this species have two distinct ear holes hidden in their fur. Males and females both have scent glands on their flanks, and females have an extra set in front of their ears. Females have six mammae along the lower body. Least shrews can be distinguished from other closely related species by both their tail length and dentition. The tail of least shrews is relatively short and measures 12 to 26 mm. Unlike related species which have three, least shrews have four unicuspid teeth, though the fourth is very small and hidden.

Range mass: 3 to 6 g.

Range length: 70 to 92 mm.

Sexual Dimorphism: sexes alike

Average basal metabolic rate: 0.164 W.

Length: 10 cm

Weight: 8 grams

See Carraway (1995) for a key to western North American soricids based primarily on dentaries.

• Terrestrial

Least shrews are most commonly found in open fields with tall grasses or areas with fallen trees and brush that provide protection. Least shrews can also be found in softer soil near saltwater marshes along the Atlantic Coast. Some occur in the forests of Florida, relying on the underbrush for cover. Least shrews have been found at elevations as high as 2,100 m.

Range elevation: 0 to 2,100 m.

Habitat Regions: temperate ; tropical ; terrestrial

Terrestrial Biomes: savanna or grassland ; forest ; scrub forest

Wetlands: marsh

Other Habitat Features: agricultural

Comments: Generally occurs in open country with dense herbaceous vegetation. Also brushy areas, forest edges, and sometimes salt and freshwater marshes. Sometimes in scrubby live oak, pine-oak, dense humid tropical forest, and cloud forest, and near water in Mexico and Central America. Nest site may be underground or under log, stump, rock, board.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Least shrews have immense dietary needs. They generally eat 60 to 100% of their own body weight every day. Least shrews are largely insectivorous, and their diet primarily consists of insect larva and centipedes. They also have been known to eat snails, spiders, and crickets. Least shrews immobilize their prey by attacking the joints of the organism so they cannot flee. The species has also been known to eat small quantities of fungi and other green plants.

Animal Foods: insects; terrestrial non-insect arthropods; mollusks; terrestrial worms

Plant Foods: leaves

Other Foods: fungus

Foraging Behavior: stores or caches food

Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)

Comments: Primarily feeds on insects and other invertebrates (e.g., earthworms, spiders), some vegetable matter.

Because of their burrowing habits, least shrews aerate soil and aid the transport of nutrients within soil. Least shrews can eat up to 100% of their body weight in a day and may contribute to regulation of insect populations. They are also eaten by a variety of predators, such as snakes and owls. Least shrews are known to host various fleas and mites such as Orycteroxenus soricis and Androlaelaps fahrenholzi.

Ecosystem Impact: soil aeration

Commensal/Parasitic Species:

• fleas Siphonaptera
• Orycteroxenus soricis
• Androlaelaps fahrenholzi

Owls are the most common predators of least shrews. Other common predators include rough-legged hawks, foxes, and snakes. Domesticated house cats and spotted skunks are also known predators. When food is scarce, least shrews may also resort to cannibalism. Their ability to stay camouflaged is the only defense of least shrews against predators.

Known Predators:

• Spotted skunk Spilogale putorius
• House cat Felis catus
• Snakes Serpentes
• Foxes Vulpini
• Rough-legged hawks Buteo lagopus
• Owls Strigiformes

Anti-predator Adaptations: cryptic

Populations may occur in small colonies. Nest is center of activity. Home range may be 3 acres (Choate and Fleharty 1973). Usually more abundant than snaptrap surveys show. Density may be 10-15 per acre (Hoffmeister and Mohr 1957, Kale 1972). Appears in owl pellets much more frequently than in traps of collectors.

Least shrews are very vocal. They make a variety of high frequency sounds including chirps and clicks, some of which are inaudible to humans. Least shrews also use ultrasonic sounds for tunnel exploration. This form of echolocation may be useful while moving underground, but there is no proof that this species uses sound to hunt. Males and females also communicate through scent. Males announce their presence to females through their scent. Females, however use their scent differently; when females stop producing pheromones, they are ready to mate. When females produce a scent, they are not ready to mate or are pregnant.

Communication Channels: acoustic ; chemical

Other Communication Modes: pheromones

Perception Channels: visual ; acoustic ; echolocation

Comments: Active day and night, probably more at night than during day.

Least shrews tend to live a little over a year in the wild. Captive least shrews, however, can live for roughly 21 months.

Range lifespan

Status: captivity: 21 (high) months.

Average lifespan

Status: wild: 1 years.

Average lifespan

Status: captivity: 2.6 years.

Mating of least shrews generally occurs within the nest. Females alert all males sharing the nest and males in adjoining areas that they are ready to mate by stopping the release of pheromones from their scent glands. When this scent is absent, males show interest by sniffing both the anal glands and glands located in front of the ears of a female. The male then attempts to mount the female. If she is unreceptive, the female may become aggressive, making loud noises and arching her back. The male then ceases its approach and lays on its back, exposing both its neck and belly until he is ready to make another attempt. Females show signs of receptiveness by lifting their tail and presenting themselves. When more than one male is present, aggression levels determine a male hierarchy, and the most aggressive males mate first. Once mating is complete, males take a dominant station over the female. The mating process on average lasts 3 days.

Mating System: polyandrous ; cooperative breeder

Least shrews may reproduce several times during the mating season, which lasts from February to November. Gestation lasts 21 to 23 days. Females give birth to an average of 5 young per litter, though litters can range from 2 to 7 individuals. Newborn least shrews weigh approximately 0.34 g. Young are weaned at about 23 days of age. Males reach sexual maturity around 43 days of age and females around 40 days.

Breeding interval: Least shrews may breed several times per year.

Breeding season: Breeding of least shrews occurs between February and November.

Range number of offspring: 2 to 7.

Average number of offspring: 5.

Range gestation period: 21 to 23 days.

Average gestation period: 21 days.

Average birth mass: 0.34 g.

Range weaning age: 21 to 23 days.

Average weaning age: 21 days.

Range time to independence: 20 to 30 days.

Average age at sexual or reproductive maturity (female): 40 days.

Average age at sexual or reproductive maturity (male): 43 days.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous ; post-partum estrous

Average birth mass: 0.34 g.

Average number of offspring: 4.5.

Average age at sexual or reproductive maturity (male)

Sex: male: 43 days.

Average age at sexual or reproductive maturity (female)

Sex: female: 40 days.

Female least shrews provide almost a full month of care to their young, which are nursed for 20 to 23 days. Most adult members within the nest take an active role in preventing juveniles from getting lost by carrying them in their mouths. Mothers show panic when separated from their young and, when reunited, gather all young together.

Parental Investment: altricial ; male parental care ; female parental care ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Provisioning: Female, Protecting: Male, Female)

Breeds March-November in north, all year in south (mainly spring-summer). Gestation lasts about 2 weeks. Litter size is 2-7, average 4-5. young are weaned in 3 weeks. Two to three litters per year. Sexually mature after 5 weeks.

A national survey in 2007 listed Cryptotis parva as a secure species in the United states. However, the state of Michigan lists least shrews as threatened. Currently, no conservation efforts are in place; little is known as to why populations are declining in Michigan.

US Federal List: no special status

CITES: no special status

State of Michigan List: threatened

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: NH - Possibly Extirpated

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

There are no known adverse effects of least shrews on humans.

Least shrews are highly insectivorous and may inadvertently help protect crops from harmful insects. Shrews also aerate soil, which is a benefit to agricultural practices.

Positive Impacts: controls pest population

Comments: Cryptotis parva formerly included, as subspecies, Central American Cryptotis orophila and C. tropicalis, which were listed as distinct species by Hutterer (in Wilson and Reeder 2005). Some of the other C. parva subspecies may be distinct species (Hutterer, in Wilson and Reeder 2005).