Eurasian wren
Two wild animal taxa are unique to St Kilda: the St Kilda wren ("Troglodytes troglodytes hirtensis"), which is a subspecies of the Eurasian wren, and a subspecies of wood mouse known as the St Kilda field mouse ("Apodemus sylvaticus hirtensis"). A third taxon endemic to St Kilda, a subspecies of house mouse known as the St Kilda house mouse ("Mus musculus muralis"), vanished entirely after the departure of human inhabitants, as it was strictly associated with settlements and buildings. It had several traits in common with a sub-species ("Mus musculus mykinessiensis") found on Mykines island in the Faroe Islands. The grey seal ("Halichoerus grypus") now breeds on Hirta but did not do so before the 1930 evacuation.