The St Kilda field mouse (''Apodemus sylvaticus hirtensis'') is 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 specie ...

of the wood mouse that 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 else ...

to the Scottish archipelago of St Kilda, the island west of

Benbecula Benbecula (; gd, Beinn nam Fadhla or ) is an island of the Outer Hebrides in the Atlantic Ocean off the west coast of Scotland. In the 2011 census, it had a resident population of 1,283 with a sizable percentage of Roman Catholics. It is in a ...

in the

Outer Hebrides The Outer Hebrides () or Western Isles ( gd, Na h-Eileanan Siar or or ("islands of the strangers"); sco, Waster Isles), sometimes known as the Long Isle/Long Island ( gd, An t-Eilean Fada, links=no), is an island chain off the west coas ...

, and from mainland Scotland. Unique to the islands, the mouse is believed to have arrived on the boats of

Viking Vikings ; non, víkingr is the modern name given to seafaring people originally from Scandinavia (present-day Denmark, Norway and Sweden), who from the late 8th to the late 11th centuries raided, pirated, traded and se ...

settlers more than a millennium ago. It is not to be confused with the

St Kilda house mouse The St Kilda house mouse (''Mus musculus muralis'') is an extinct subspecies of the house mouse found only on the islands of the St Kilda archipelago of northwest Scotland. They were first described, alongside the St Kilda field mouse, by natu ...

(''Mus musculus muralis''), a subspecies of the

house mouse The house mouse (''Mus musculus'') is a small mammal of the order Rodentia, characteristically having a pointed snout, large rounded ears, and a long and almost hairless tail. It is one of the most abundant species of the genus ''Mus''. Although ...

which is now extinct. The last remaining human inhabitants of St Kilda abandoned the islands on 29 August 1930. Thereafter the mice that survived, even those occupying houses abandoned by the St Kildans, were field mice that had moved into the houses from the hills. The islands' house mice could not survive the harsh conditions for more than two years after the archipelago was abandoned by its human population. The islands currently have temporary human habitations. While field mice are widespread on

Hirta Hirta ( gd, Hiort) is the largest island in the St Kilda archipelago, on the western edge of Scotland. The names (in Scottish Gaelic) and ''Hirta'' (historically in English) have also been applied to the entire archipelago. Now without a perman ...

, their concentration is more pronounced in the old village areas where holes provide access into buildings. Though rarely observed by casual visitors, the mouse is common and is present in every part of the habitat, from the harbour to the high point.

Description

The mouse has black eyes, small peaked ears, and is fairly uniform in colour: mainly brown, with a lighter shade of fur on its underside. It is generally twice as heavy as field mice found on the mainland, with a mass of between and , and has longer hair and a longer tail. The evolution of a larger size has been credited to a lack of predators in its island habitat, which allows the mice to grow larger to preserve heat and increase fat storage. The mouse can reach a maximum length of about . It is found across the main island, Hirta, especially in the remains of human settlements, as well as on the island of Dùn. It is not found on Boreray. Studies of the fur of the mice have recorded the

flea Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, ...

species ''Ctenophthalmus nobilis'', and ''Nosopsyllus fasciatus'' on the mouse as well as the mite ''Typhloceras poppei''. Studies of the intestines have observed the

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant- parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a bro ...

''Tictularia cristata'' and the

cestode Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of ...

''Hymenolepsis diminuta''.

Diet

The mouse is an opportunistic

omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...

. Its diet includes insects, snails, seeds, and moss, as well as human litter and animal carcasses. With only one other native mammal, the Soay sheep, which eats grasses and herbs, the St Kilda field mouse faces little competition for food on the islands.

History

Unique to the islands, the ancestors of the St Kilda's field mouse are believed to have arrived on the ships of

settlers. The

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

was first described in 1899 by

Gerald Edwin Hamilton Barrett-Hamilton Major Gerald Edwin Hamilton Barrett-Hamilton (1871 – 17 January 1914) was a British/Irish natural historian, co-author with M. A. C. Hinton of ''A History of British Mammals'', which remained "the most thorough, accurate and scientific public ...

as the separate species ''Apodemus hirtensis''. A year later in a specific review of mouse species the taxon was reclassified as a

of the wood mouse ''

Apodemus sylvaticus The wood mouse (''Apodemus sylvaticus'') is a murid rodent native to Europe and northwestern Africa. It is closely related to the yellow-necked mouse (''Apodemus flavicollis'') but differs in that it has no band of yellow fur around the neck, ha ...

''. Studies of the mouse populations on the islands were carried out in 1931, 1939 and 1955. These studies documented the rapid extinction of the endemic house mouse subspecies (which was dependent for its survival on grain and other commodities used by the islands' human inhabitants), and its subsequent replacement by the field mouse, through a process of

niche expansion Colonisation or colonization is the process in biology by which a species spreads to new areas. Colonisation often refers to ''successful'' immigration where a population becomes integrated into an ecological community, having resisted initia ...

References

{{DEFAULTSORT:Saint Kilda field mouse Apodemus Rodents of Europe Fauna of St Kilda, Scotland Endemic fauna of Scotland Endemic biota of the Scottish islands Mammals described in 1899 Taxa named by Gerald Edwin Hamilton Barrett-Hamilton