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Humans, House Mice, and Habitats

Isolated from their mainland relatives, these house mice evolved over time into a distinct species, larger and shaped differently from their ancestors.

Gray house mouse

Photo: Lynette S. (flickr)

House mice depend on humans for survival

We often hear about how human activity and expansion can endanger wildlife habitats. But can you think of any animals that might be threatened by the disappearance of humans? After careful consideration, the story of the extinct St. Kilda House Mouse came to my mind.

St. Kilda is a small group of islands about one-hundred miles off the west coast of Scotland. The isolated archipelago was inhabited by humans for more than two thousand years, from the Bronze Age until 1930. In 1930 the few remaining residents of St. Kilda were permanently evacuated because of sickness, crop failure, and casualties of World War I.

Scientists believe that as early as 500 BC, Norse settlers arrived in St. Kilda and brought along a few unwanted stowaways–European house mice. Isolated from their mainland relatives, these house mice evolved over time into a distinct species, larger and shaped differently from their ancestors. St. Kilda is also home to a unique subspecies of field mouse, that probably also arrived as stowaways and evolved into a new species.

But the St. Kilda house mouse needed the warm houses, farms, and dropped food crumbs of its human neighbors to survive. Within three years of the humans evacuating, all the St. Kilda house mice had died off. In contrast, the field mice survived and are still living on St. Kilda today.

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