The siblings, aged between three days old and one week old, originated from the Island of North Ronaldsay, Orkney.
They maintain the flock book, established in 1974, which is the breed registry containing all purebred animals. This book reports that there are fewer than 600 breeding females and roughly 3700 sheep in total. The Rare Breeds Survival Trust (RBST) lists the North Ronaldsay as "vulnerable".
They have unusual speckled coats and are one of the rarest sheep breeds in Britain.
The North Ronaldsay Sheep lives largely on a diet of seaweed, and the Boreray – which lives only on the St Kilda archipelago – is the UK's rarest sheep, having been listed as "Category 2: Endangered" by the RBST.