The Scottish crossbill, "Loxia scotica", which inhabits the coniferous forests of the Highlands, is Britain's only endemic bird and, with only 300 breeding pairs, one of Europe's most threatened species. Its shape, red/green hue and habit of hanging upside down has led to comparisons with parrots. St Kilda has a unique subspecies of wren, the St Kilda wren "Troglodytes troglodytes hirtensis", which has adapted to perching on the rocks and cliffs of this treeless Atlantic island, and consequently has developed larger and stronger feet than the mainland variant. It is also slightly larger, has a longer beak, a drabber though more varied colouring, and a "peculiarly sweet and soft" song. The subspecies was recognised in 1884 and was protected by a special Act of Parliament in 1904 to prevent its destruction "at the hands of ornithologists, egg-collectors, taxidermists and tourists".