North Ronaldsay Sheep: Wool Shaped by the Sea

On North Ronaldsay, the northernmost island in Scotland's Orkney archipelago, a small breed of sheep survives almost entirely on seaweed. This diet is found in almost no other land mammal. The habit is not really a natural preference. It is a forced adaptation. In 1832, islanders built a six-foot drystone wall around the entire coastline. The wall kept the sheep off farmland that had recently been reorganized, restricting them instead to the coastline. Cut off from grass for most of the year, the sheep gradually adapted to survive on the seaweed exposed twice a day by the tide. Their digestive system became more like that of an animal that grazes on marine algae, rather than an ordinary pasture-fed sheep. This diet is unusually rich in minerals absorbed from the seaweed. It also appears to change the resulting wool. The fleece is naturally more resistant to fire than typical sheep's wool. It also grows as a double coat: a coarse, weatherproof outer layer protects a much finer, softer undercoat beneath. Hand-spinners and small textile mills prize the soft undercoat for warm, durable knitting yarn. The coarser outer fibers, meanwhile, are worked into tweed and woven cloth. This gives a rare breed, shaped by isolation and necessity, a continuing, practical life in craft textiles.