The beach vole (''Microtus breweri'') or Muskeget vole is a

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

in the family

Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and has m ...

. This close relative of the

eastern meadow vole The eastern meadow vole (''Microtus pennsylvanicus''), sometimes called the field mouse or meadow mouse, is a North American vole found in eastern Canada and the United States. Its range extends farther south along the Atlantic coast. The west ...

(''Microtus pennsylvanicus'') is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the 0.87km²

Muskeget Island Muskeget Island is a low sandy island to the west of Tuckernuck Island and Nantucket, in the town of Nantucket, Massachusetts, United States. Geography Muskeget Island is part of the terminal moraine marking the maximum extent of the last glaci ...

Massachusetts Massachusetts (Massachusett language, Massachusett: ''Muhsachuweesut assachusett writing systems, məhswatʃəwiːsət'' English: , ), officially the Commonwealth of Massachusetts, is the most populous U.S. state, state in the New England ...

. Due to its relatively short period of

reproductive isolation The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring ...

, there is debate over the beach vole’s designation as a

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...

of ''M. pennsylvanicus''.

Taxonomy

''M. breweri'' is currently recognized by the IUCN, NatureServe and ITIS as a distinct species, due to its larger size, geographic isolation, and contrasting mating habits. A recent genetic study indicates that it may be a basal subspecies of ''M. pennsylvanicus''.

Description

Beach voles are typically much larger than meadow voles. On average, male beach voles are 192.9 mm long, ranging between 169 to 215 mm; with the tail making up approximately one-fourth of the total length. Generally, females are smaller, with an average length of 181.2 mm, ranging between 165 to 201 mm. The weight of a beach vole ranges between 29-79 g, proportional to age, with females weighing less than males. Compared to meadow voles, beach voles exhibit a lower

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

, and their

coat A coat typically is an outer garment for the upper body as worn by either gender for warmth or fashion. Coats typically have long sleeves and are open down the front and closing by means of buttons, zippers, hook-and-loop fasteners, toggles, a ...

is made up of more guard hairs and fewer underhairs. A white blaze can often be found on the chin or forehead. The

skulls The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

of ''M. breweri'' can be easily distinguished from those of meadow voles. The average cranial length of beach voles is 13.1 mm, while the cranial breadth is generally 11.2 mm. Their skull is larger, and their

brain case In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

is longer and narrower than meadow voles. Recent unpublished observations include a distinctly shaped

interparietal bone An interparietal bone (os interparietale or Inca bone or ''os inca var.'') is a dermal bone situated between the parietal and supraoccipital. It is homologous to the postparietal bones of other animals. In humans, it corresponds to the upper p ...

and a narrow bridge between the

orbits In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

. Beach voles tend closer towards

K selection In ecology, ''r''/''K'' selection theory relates to the natural selection, selection of combinations of Trait (biological), traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity ...

than meadow voles, and some of their distinctive features are indicative of

island gigantism Island gigantism, or insular gigantism, is a biological phenomenon in which the size of an animal species isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general "i ...

Distribution

''M. breweri'' can only be found on Muskeget Island, off the west coast of Nantucket, Massachusetts, in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

. However, historically it was also found on nearby South Point and Adams Islands, which are sometimes considered as a part of Muskeget Island, but are no longer above

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...

. The vole was

extirpated Local extinction, also known as extirpation, refers to a species (or other taxon) of plant or animal that ceases to exist in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinct ...

from Muskeget proper by 1891 as a result of

predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

by stray

cats The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of t ...

(''Felis catus''), but was reintroduced by Gerrit S. Miller,

Outram Bangs Outram Bangs (January 12, 1863 – September 22, 1932) was an American zoologist. Biography Bangs was born in Watertown, Massachusetts, as the second son of Edward and Annie Outram (Hodgkinson) Bangs. He studied at Harvard from 1880 to 1884, and be ...

, and Chas F. Batchelder in 1893 from a colony captured on South Point Island. Moreover, Muskeget Island has moved about 1,000 feet eastwardly over the last about 200 years, along with its changing process of shape, size and position due to

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

and tidal buildup.

Habitat and diet

These voles dominate an open habitat of poison ivy (''Toxicodendron radicans'') and

beach grass ''Ammophila'' (synonymous with ''Psamma'' P. Beauv.) is a genus of flowering plants consisting of two or three very similar species of grasses. The common names for these grasses include marram grass, bent grass, and beachgrass. These grasses ar ...

(''Ammophilia breviligulata''). Swaths of bare sand and saltwater marsh can be found on the island, but the voles tend to avoid these areas. They may burrow in loose sand or loose soil under or near any of their shelters. '' M. breweri'' feeds on beach grass stalks, leaves, seeds, and insect adults and

larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

. Their predators include birds of prey such as the

short-eared owl The short-eared owl (''Asio flammeus'') is a widespread grassland species in the family Strigidae. Owls belonging to genus ''Asio'' are known as the eared owls, as they have tufts of feathers resembling mammalian ears. These "ear" tufts may or ...

(''Asio flammeus'') and the

northern harrier The northern harrier (''Circus hudsonius''), or ring-tailed hawk, is a bird of prey. It breeds throughout the northern parts of the northern hemisphere in Canada and the northernmost USA. The northern harrier migrates to more southerly areas ...

(''Circus hudsonius''). Cats were introduced onto Muskeget in the late 1800s, decimating the vole’s population, but are no longer present. Their home range is usually less than one acre.

Reproduction and behavior

Young beach voles are born in the

burrow An Eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of sh ...

nests A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materi ...

, underneath fragments of

wreckage Wreckage may refer to: * Debris Music * ''Wreckage'' (album), a 2002 album by Overseer * ''Wreckage'' (1969 band), a late 1960s band notable for featuring future Queen vocalist Freddie Mercury as a member * ''Wreckage'', a 1997 EP by the band E ...

, or at the base of

goldenrod Goldenrod is a common name for many species of flowering plants in the sunflower family, Asteraceae, commonly in reference to the genus ''Solidago''. Several genera, such as ''Euthamia'', were formerly included in a broader concept of the genus ...

(''Solidago'' sp.). They do not demonstrate a typical vole breeding cycle, and show many of the attributes of a K-selected organism, such as large size, later age at maturation,

sex ratio The sex ratio (or gender ratio) is usually defined as the ratio of males to females in a population. As explained by Fisher's principle, for evolutionary reasons this is typically about 1:1 in species which reproduce sexually. Many species devia ...

weighted towards the males, and low reproductive output. The adults can breed from the spring to the fall, and their

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...

lasts for about one month. Every year, an individual female beach vole typically produces two litters of three to five offspring, but most will live for less than one year. The beach voles have a habit of building runways above or in the ground under the beach grass, in order to better stay hidden from aerial predators. These runways may contain cut grass. During winter, underground tunnels become more common due to the cold weather.

References

External links

* http://training.fws.gov/library/pubs5/necas/web_link/39_muskeget.htm Subspecies Microtus Mammals described in 1858 Martha's Vineyard Nantucket, Massachusetts Taxa named by Spencer Fullerton Baird Taxonomy articles created by Polbot {{Microtus-stub