 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 completely after the departure of human inhabitants , as it was strictly associated with settlements and buildings . It had a number of 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 . 
