Terrestrial

The terrestrial biology of the St Kilda archipelago provides an outstanding example of remote island ecological colonisation and subsequent genetic divergence under isolation, it is unique within the Palaearctic Realm and is significant at the global level. Isolation and genetic divergence are notable within small mammal (fieldmouse), non-seabird (wren) and large mammal (sheep) populations. The unique feral Soay sheep are descendants of the most primitive domestic form in Europe, resembling the original wild species and the domesticated Neolithic sheep.

The terrestrial fauna and flora show low species diversity but the islands have large breeding populations of certain species (seabirds). The isolated mammal and bird populations provide the basis for ongoing research into island ecosystems.

Roseroot and sea pink

As the most remote archipelago in Great Britain and Ireland, St Kilda presents the most extreme example of restricted island flora and fauna. Only nine species of land birds breed there annually for example, compared with 17 seabirds. The same can be said for other animal groups, such as Lepidoptera and Hymenoptera.

Overall, the flora of St Kilda is extremely impoverished due to its small size, its isolation and restricted habitats (no trees or shrubs for instance, and little freshwater). Only 184 species of ferns, flowers and grasses have been recorded on St Kilda, and only 170 species of fungi. Several plants appear to occupy a wider range of ecological niches on St Kilda than they do on the mainland, a phenomenon not uncommon in isolated archipelagos and known as ‘niche

expansion’. St Kilda is, however, surprisingly rich in some lower plants, with 194 species of lichen and 160 species of bryophyte. One of the most striking features of the bryophyte flora is the abundance of the extreme oceanic and somewhat salt-tolerant liverwort Frullania teneriffae all over the island.

The feral Soay sheep of St Kilda are descendants of the most primitive domestic form in Europe, resembling the original wild species and the domesticated Neolithic sheep that were first brought to Britain about 7,000 years ago. Another flock of primitive blackface sheep survives on the island of Boreray, unmanaged since the islands were evacuated by the human inhabitants in 1930.

The most notable land bird resident is St Kilda's own distinctive subspecies of wren which shows characteristics that may be adaptations to island conditions. The St Kilda fieldmouse, possibly introduced to the islands by the Vikings, also displays evolutionary changes (compared with its mainland counterpart) that meet the unusual and rigorous conditions presented by the archipelago.