Sixty per cent of all breeding bonxies nest in Scotland, mostly in Orkney and Shetland, even though they did not arrive at all until the 18th century. Scotland is the breeding station for about 90% of the UK's Arctic terns, the majority of which make use of colonies in Orkney and Shetland. A similar percentage of the UK's tysties breed on Scottish islands including Unst, Mingulay and Iona. Scotland also hosts 1,000 pairs of Arctic skua and 21,000 breeding pairs of shag, 40% of the global population of the species.