St Kilda Field Mouse

About 100 kilometers west of the Scottish coast lies St Kilda, a remote mini-archipelago of which Hirta (Hiort in Scottish Gaelic) is the main island. Hirta. Only Hirta was once inhabited, its population probably never exceeding 180 and was slowly declining for decades. The entire remaining population of 36 intensely sombre and religious men and women was evacuated from Hirta in 1930. They were transferred to mainland Scotland, where they became even more unhappy because they missed their own little place under the sky[1].

[Image Jackhynes][St Kilda Field Mouse]

These days St Kilda is a nature reserve and is an important breeding ground for many species of seabird. But, hidden from sight, a unique species of field mouse also lives on St Kilda. The St. Kilda field mouse (Apodemus sylvaticus hirtensis) is a subspecies of the wood mouse (Apodemus sylvaticus) that is only endemic to the archipelago of St. Kilda. The mouse is unique to the islands and is believed to have arrived on the boats of Viking settlers more than a millennium ago.

Because no predators exist on St Kilda, this subspecies was able to grow to twice the size of its ancestor, the field mouse. The St. Kilda field mouse generally weighs between 50 grams and 70 grams. It has black eyes, small peaked ears, and is fairly uniform in colour: mainly brown, with a lighter shade of fur on its underside. It also has longer hair and a longer tail. The St Kilda field mice can survive by eating snails, insects, moss and seeds, can feed on the carcasses of dead sheep and birds, but and will also readily eat food brought in by visitors and intended for their own consumption.

The increased size enables the St. Kilda field mouse to preserve its heat and increase fat storage, something that is necessary in the harsh clime of St Kilda.

When the archipelago was abandoned by its human population and their houses were no longer heated, none of the islands' house mice could survive the bleak conditions and all perished within two years.

[1] Boudewijn Büch: Eilanden -1991