Competition and extinction: the mice of Foula, with notes on those of Fair Isle and St Kilda

House mice ( Mus rnusculus muralis ) on St Kilda became extinct within about 18 months of the human population leaving the island in 1930. Although it was argued at the time that they died out because they were unable to find enough food, house mice flourish on a number of uninhabited islands and it seems more probable that they could not successfully compete with the Long-tailed field mouse ( Apodemus sylvaticus ) in the absence of man.
A study of the distribution and diet of both house and field mice on the Shetland islands of Foula and Fair Isle shows that the house mouse populations tend to be centred on human dwellings, although both species were found apparently living together on Foula away from habitation. The natural history of the two species is reviewed, and it is concluded that the breeding of the house mouse is the most probable characteristic to be upset by disturbance, and that the disappearance of man on St Kilda allowed Apodemus to enter a habitat previously occupied almost exclusively by Mus .