Because of the low capture rate of S. hoyi in the field, relatively little information is available regarding the natural history of this species. Most of the information available is fragmentary and anecdotal.
The vocal communication of these animals has been described as a combination of sharp squeaks, low purrs, and high-pitched whistling. The role of these calls in the species is not known.
In addition to vocal communication, these animals are known to produce strong smells from scent glands when they are frightened or excited. This indicates that scents may be important in communication. This is likely to be especially true of individuals identifying potential mates.
Physical contact probably occurs between rivals, mates, and between mothers and their offspring. It is likely that some tactile communication occurs at these times.
Because of their tiny eyes, it is unlikely that visual cues play a large role in the communication of these animals.
Communication Channels: tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; acoustic ; chemical
It is unclear whether low capture rates for pygmy shrews indicates low population densities of these animals. The low capture rates may be caused by inadequate trapping techniques.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Little information is available regarding the negative impact pygmy shrews have on humans. They may prey on beneficial organisms, such as earthworms. However, Baker (1983) suggests that these small mammals have no real impact on humans.
The extent to which these animals affect humans is unknown. They potentially affect pest populations through predation. However, Baker (1983) suggests that there is no real impact of these animals on humans.
Because they are widespread, pygmy shrews probably have significant impact on their ecosystems. They are predators, and are likely to have some role regulating invertebrate populations. To the extent that these animals serve as food for others, they may also be important to these predators.
Commensal/Parasitic Species:
Pygmy shrews usually eat insects and other invertebrates. The diet includes ants, flies, spiders, earthworms, beetles, grubs, and caterpillars. Captive pygmy shrews have been known to eat dead vertebrates, such as masked shrews, red-backed voles and white-footed mice.
Animal Foods: mammals; amphibians; carrion ; insects; terrestrial non-insect arthropods; terrestrial worms
Primary Diet: carnivore (Insectivore )
Pygmy shrews, Sorex hoyi, are distributed throughout the boreal region of North America. The northern extent of the species' geographic range spans from Alaska to the east coast of Canada south of the tundra. It ranges as far south as the Rocky Mountains of Colorado and the Appalachian Mountains of the northeastern United States.
Biogeographic Regions: nearctic (Native )
Sorex hoyi, although rare locally, occupies a wide variety of habitat types throughout its range. These include coniferous and deciduous forests, swamps, grassy clearings, bogs and floodplains. An equally wide array of microhabitats is acceptable to these animals. Sorex hoyi has been found in diverse microhabitats such as sphagnum moss, moist soil, mammalian tunnel networks, insect tunnel networks, leaf litter, root systems, and stumps.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: forest ; mountains
Wetlands: bog
Other Habitat Features: riparian
One male shrew is known to have lived 11 months after hsi capture. It is not known how old he was at the time of capture. Most shrews captured are young, so it is reasonable to assume that not many shrews grow to be very old. It is likely that the maximum lifespan of pygmy shrews in the wild is about two years.
Sorex hoyi (formerly known as Microsorex hoyi) is the smallest American mammal by weight, weighing in at only 2 to 4 g. These shrews are approximately 80 to 91 mm in total length. The tail accounts for approximately 1/3 of that length at 27 to 32 mm. The head is narrow, the nose pointed, and there are obvious whiskers. The eyes are inconspicous, being covered by short, soft fur. Dorsal coloration varies from gray-brown in the summer to gray in the winter. The underparts are a lighter gray. The dental formula is: 3/1, 1/1, 3/1, 3/3 = 32.
Range mass: 2 to 4 g.
Range length: 27 to 32 mm.
Other Physical Features: endothermic ; bilateral symmetry
The musky secretions which ooze from flank glands when a shrew is upset seem to deter most predators. However, there are reports of pygmy shrews being taken by brook trout, garter snakes, hawks, and house cats.
Known Predators:
Little is known about the reproductive habits of these animals.
Information regarding the reproductive biology of S. hoyi is limited. Based on the condition of the reproductive glands in males throughout the year, the mating season of this shrew is from June through August. The gestation period is estimated to be about 18 days. Females produce one litter of 3 to 8 young per year. Time until weaning and independence are unknown. Juveniles reach sexual maturity in their second summer.
Pygmy shrews seem to mate from June to August. Pregnancy lasts about 18 days. Females give birth to one litter of 3 to 8 young per year. The length of dependence on the mother is unknown. Juveniles are able to breed in their second summer.
Breeding interval: These animals are likely to produce one litter per year.
Breeding season: Breeding occurs from June to August.
Range number of offspring: 3 to 8.
Average gestation period: 18 days.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Because so little is known about the reproduction of these animals, it is difficult to speculate on parental care. Because they are mammals, we know that S. hoyi females provide their young with milk. It is likely that they also provide shelter and protection for some period of time. The length of juvenile dependence is unknown, as is the role of males in parental care.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female)
The American pygmy shrew (Sorex hoyi) is a small shrew found in Northern Alaska,[4] Canada, and the northern United States, south through the Appalachian Mountains. It was first discovered in 1831 by naturalist William Cane in Georgian Bay, Parry Sound.
This animal is found in northern coniferous and deciduous forests of North America. It is believed to be the second-smallest mammal in the world, but has an extremely large appetite for its size. Due to its fast metabolism, it needs to eat constantly. It digs through moist soils and decaying leaf litter for food.
The American pygmy shrew is the smallest mammal native to North America and is one of the smallest mammals in the world, being just slightly larger than the Etruscan shrew of Eurasia. Its body is about 5 cm (2 in) long including a 2-cm-long tail, and it weighs about 2.0 to 4.5 g (0.07 to 0.16 oz).[5] Its fur is generally a reddish or grayish brown during the summer, and a white-gray color during the winter. The underside is generally a lighter gray. This animal molts about twice a year, once during late summer, and again during the spring.[6] It has a narrow head with a pointed nose, and whiskers. The eyes are small and well hidden.[7] The primary senses used for hunting are hearing and smell.
Sorex hoyi was originally placed in the genus Microsorex, which was a subgenus under Sorex until more research had been done. The American pygmy shrew is in the order Soricomorpha and the family Soricidae. Its two closest relatives are the smokey shrew (S. fumes) and the large-toothed shrew (S. macrodon). This genus is believed to have appeared in the late Miocene.
Pygmy shrews are distributed throughout the boreal areas of North America. This ranges from Northern Alaska,[4] to the Rocky Mountains, through the Great Lakes region, to the Appalachians, to the eastern side of Canada.[7] Although S. hoyi prefers moist habitats, it has been recorded to live in areas with both wet and dry soil, but if it is living in a more arid environment, it needs to have a source of water nearby.[6]
Primarily insectivorous, this animal forages in moist soil and dead leaves to find its prey. Because of the pygmy shrew's small size, its diet primarily consists of insects and insect larvae, while the larger shrews eat insects and worms.[8] Its diet is almost exclusively protein-based.[9] To stay alive, the pygmy shrew has to eat three times its body weight daily, which means capturing prey every 15 to 30 minutes, day and night; a full hour without food means certain death. Because of this high metabolism, the pygmy shrew never sleeps more than a few minutes at a time, as it is in a constant search for food.[5] Although due to its small body size it is always losing body heat, being small has its advantages during the winter when food is scarce. Predators of the American pygmy shrew include hawks, brook trout, owls, snakes, and domestic cats.
Little is known about the reproductive cycle of pygmy shrews. They appear to mate year round, with a bias of births occurring from November through March.[10] The gestation period is estimated to last about 18 days.[7] Females produce a litter of three to eight young, and only give birth once a year. The age the young are weaned is not known with certainty, but by 18 days old, they are nearly full grown, and are usually independent by 25 days.[10] Being mammals, the mother nourishes her young with milk. The maximum lifespan of a pygmy shrew is not known, but it is believed to be about 16–17 months.[10]
Pygmy shrews dig through soil and leaf litter to search for food, and can use tunnel networks created by other animals to aid in that search. They do not sleep or rest for extended periods of times, but alternate between rest and activity all day and night, showing a bias towards nighttime.[9] They have keen senses of smell and hearing to help them find prey.[7] When feeling threatened or scared, the shrews make a sharp squeaking noise and run for cover. Shrews can also swim, which makes them prey to brook trout. Pygmy shrews are in constant motion, and captured shrews have been observed "climbing and walking upside down on the wire top of the cage."[6]
Due to its high metabolism, the pygmy shrew is active year-round and does not engage in any form of torpor. Shrews have been known to burrow through snow to find food, showing that winter snow does not stop them. Although usually a positive correlation exists between latitude and shrew body size, the American pygmy shrew is an exception. Although it is constantly losing body heat because it is so small, it also benefits from this because to generate that energy takes less food than it would for a larger shrew.[8]
The American pygmy shrew (Sorex hoyi) is a small shrew found in Northern Alaska, Canada, and the northern United States, south through the Appalachian Mountains. It was first discovered in 1831 by naturalist William Cane in Georgian Bay, Parry Sound.
This animal is found in northern coniferous and deciduous forests of North America. It is believed to be the second-smallest mammal in the world, but has an extremely large appetite for its size. Due to its fast metabolism, it needs to eat constantly. It digs through moist soils and decaying leaf litter for food.
