Eastern harvest mouse

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Eastern harvest mouse
Fossil range: Irvingtonian to present
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Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Genus: Reithrodontomys
Species: R. humulis
Binomial name
Reithrodontomys humulis
(Audubon & Bachman, 1841)
Synonyms
R. carolinensis (Audubon and Bachman, 1842)
R. dickinsoni Rhoads, 1895
R. impiger Bangs, 1898
R. lecontii (Audubon and Bachman, 1842)
R. merriami J. A. Allen, 1895
R. virginianus A. H. Howell, 1940

The eastern harvest mouse (Reithrodontomys humulis) is a species of cricetid Mouse found in North America. It is small, one of the smallest Rodents in the world, with a short, slender tail and brown Fur. It is found in grassy fields, brier patches, roadside ditches, and marshlands. Its diet consists of weed seeds, green plants, insects, and possibly the Larvae of Moths and butterflies. The mouse builds a Baseball-sized, globular nest of shredded grasses and plant fibers several Centimeters above the ground in upright water plants or the tangled vegetation beneath fences. The mouse is Nocturnal, does not store food, and does not Hibernate. Pregnancies are frequent, litter size is two to four, and the young attain adulthood in approximately seven weeks. Predators include Snakes, Barn owls, and small Carnivores such as Foxes. Lifespan is believed to be less than a year.

Contents

Taxonomy and etymology

The eastern harvest mouse is one of the smallest rodents in the world,[2] and is the smallest of all living North American harvest mice.[3] Its adult weight range is 6.5–12 g (0.23–0.42 oz).[4] The species is distinguished from the House mouse and the mice of the genus Peromyscus by deeply grooved Upper incisors.[2] The first and second lower Molars of the eastern harvest mouse show a prominent labial shelf or ridge, often with prominent cusplets.[2]

The species is known mostly by Biologists, and the common name is probably inspired by the animal's habit of harvesting seeds.[2] John James Audubon and John Bachman described the mouse in 1841 in "Descriptions of new species of quadrupeds inhabiting North America" for the Academy of Natural Sciences of Philadelphia, Pennsylvania.[5] Fossil specimens found in Florida date to as far back as the late Irvingtonian.[3]

Description

The upperparts of the eastern harvest mouse are rich, dark brown mixed with cinnamon or gray (darkest mid-Dorsum), and its underparts are ashy with cinnamon or pinkish touches. The sides are paler than the dorsum and a lateral line is distinctly visible. The tail is relatively short (shorter than the head and body), slender, sparsely furred,[6] brownish-gray above and paler below. The feet are pale gray, and the ears brownish-gray or blackish. Whitaker describes the mouse as a "dainty little creature". Its population is probably larger than collected specimens indicate but the population is never very large.[7] Maximum lifespan is not yet established, but in captivity they live on average 2.2 years, and in the wild less than one year.[8][9]

Measurements [4]
Length120 mm (4.7 in) 115–132 mm (4.5–5.2 in)[4]
Tail56 mm (2.2 in) 52–65 mm (2.0–2.6 in)[4]
Hind foot16 mm (0.63 in) 11–18 mm (0.43–0.71 in)[4]
Ear8–9 mm (0.31–0.35 in)[10]
Weight6.5–12 g (0.23–0.42 oz)[4]
Diploid numberUnknown[4]
Tooth formula = 16[4]

Distribution and habitat

The eastern harvest mouse is native to North America,[1] and occurs in the Southeastern United States from southeastern Texas and Oklahoma in the west to peninsular Florida (except the southernmost reaches) in the south and Kentucky, north-central Ohio, West Virginia, and Maryland in the north.[4][10] A small population occurs in northwestern Arkansas.[4] Deforestation and the growth of agriculture in recent history have created suitable habitat for the species and the population and its range have expanded.[1][11]

The mouse prefers damp habitats and rarely occurs in forested situations.[5] Waste fields of matted grasses and broom Sedge, tangled Brier patches, roadside ditches, grassy flatlands, abandoned agricultural fields, prairie, meadows, and marshlands are preferred and shared by the eastern harvest mouse with meadow mice, Least shrews, and golden mice.[1][4][6] The eastern harvest mouse requires ample ground cover. The home range is probably less than 0.4 Ha and in Virginia, maximum observed density was 44/ha in winter.[1] It is the only Harvest mouse in much of its range.[12] The mouse is not especially abundant with only two or three per Acre.[10]

Behavior

The eastern harvest mouse is Nocturnal, except in Winter when foraging may take place in the warmer daylight hours. It is not particularly Territorial and tolerates others.[10]

Diet

Eastern harvest mice feed on the numerous small weed seeds available throughout the year in their range, and may feed on lepidopterous larvae. The mice do not store seed to any extent, and, at the minimum, might store witch grass, Crabgrass, and brown Sedge seeds. Evidence suggests the female may gather food to her nest just before giving birth.[13] The mice will eat some green vegetation and insects.[5][10]

Shelter

Eastern harvest mice build small nests of shredded plant fibers and grasses in the tangled herbage beneath a fence, or at the base of a clump of grass or shrubs.[5][14] The nest may be built several Centimeters above the ground in a shrub or in upright water plants and rushes above wet ground. The nest has one entrance, and the nest serves its inhabitant(s) through the entire year,[5][14] for the species does not hibernate.[14] Nests are Baseball-sized globes and, in cold weather, six or more mice will huddle together in a single nest to conserve energy. A mouse may have two to four nests located at the periphery of its home range. The species does not Burrow but may use burrows belonging to other animals in cold weather.[10] Eastern harvest mice do not make runways and passageways but often use those of others.[14]

Reproduction

Breeding begins in March with a lull in Midsummer. In South Carolina, pregnant females have been observed in December and pregnancies are apparently year-round occurrences in Florida. Frequent pregnancies suggest mating occurs soon after Partuition.[15] Young are born in spring, Summer, and early Autumn.[5]

A female taken in Florida produced eight litters in captivity in eleven months. Once pregnant, she gained weight quickly in the third and fourth days before giving birth. The young averaged 1.2 g (0.042 oz) 0.8–1.6 g (0.028–0.056 oz) at birth and gained about one gram per week in the first three weeks of life until weight leveled off at a weekly gain of 0.4 g (0.014 oz) over the following four weeks. Adult measurements were realized at about seven weeks.[15]

Newborn length was 35–38 mm (1.4–1.5 in), tail length 10–11 mm (0.39–0.43 in), and hindfoot length 5–6 mm (0.20–0.24 in). At three weeks, the same measurements were 90–110 mm (3.5–4.3 in), 45–50, and 14–15 mm. Eyes and ears opened between the seventh and tenth days, and the young looked like harvest mice at the end of the second week. Adult coloration was evident the seventeenth day. Lower incisors were visible by the seventh day, and fully developed by the end of the third week.[15]

Reported litter sizes range from one to five young, but, in October 1959, a litter numbering eight young was reported. The mother weighed 17 g (0.60 oz) and was caged alone. The young ranged in weight from 0.82–1.12 g (0.029–0.040 oz). All fell victim to the mother's Cannibalism within two days but not all were completely consumed.[16]

The mother protects the young for the first three weeks and pulls them into the nest away from danger. In caged situations studied, males offered some protection to the young and one was observed pulling a young into the nest, but males are generally excluded from the maternal nest and build separate nests. Weanings and excursions from the nest with the young occurred between the second and fourth weeks in the caged situations.[13]

Life history traits (averages)[8]
Sexual dimorphismNone
Female sexual maturity105 days
Male sexual maturity
Gestation23 days; 21– 22 days [13]
Weaning23 days
Litter size2.9 (Viviparous);1– 5 (usually 2– 3)[13];2– 7 (4 average)[5]
Litters per year
Inter-litter interval32 days
Weight at birth1.115 g
Weight at weaning
Adult weight10.3 g
Postnatal growth rate0.0694 days-1
(from Gompertz function)

Survival

Carnivorous animals and birds that hunt in Meadows are assumed to prey upon these mice.[13] Snakes are predators,[10] and Barn owls are known to be heavy predators. In 1998, researchers had yet to provide adequate information on Parasites and Diseases of the species, but four species of Mites have been recorded and a host-specific Louse may be involved.[13] Internal Helminths and small Arthropods parasitize the mouse.[10]

Conservation

In 2008, the IUCN listed the eastern harvest mouse as of Least Concern because it is "very widespread, common in suitable habitat in most parts of its range, and there are no major threats." Its range includes several protected areas.[1]

The eastern harvest mouse is not abundant in cultivated areas and the mouse poses little harm to human interests. Its consumption of weed seeds and lepidopterous larvae is beneficial to humans.[13]

References

Footnotes
  1. ^ a b c d e f Linzey and NatureServe, 2009
  2. ^ a b c d Whitaker 282
  3. ^ a b Kurtén 240
  4. ^ a b c d e f g h i j k Whitaker 285
  5. ^ a b c d e f g Eastern Harvest Mouse
  6. ^ a b Kays 110
  7. ^ Whitaker 284
  8. ^ a b Reithrodontomys humulis
  9. ^ Stalling 4
  10. ^ a b c d e f g h Jones 186
  11. ^ Stalling 1
  12. ^ Bowers 186
  13. ^ a b c d e f g Whitaker 286
  14. ^ a b c d Whitaker 285-6
  15. ^ a b c Whitaker 286
  16. ^ Dunaway
Works cited

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