It was formerly kept primarily for wool, but now the two largest flocks are feral, one on North Ronaldsay and another on the Orkney island of Auskerry.

They are confined to the foreshore by a 1.8 m (6 ft) early 19th century drystane dyke, which completely encircles the island, forcing the sheep to evolve this unusual characteristic.

Sheep were confined to the shore to protect the fields and crofts inside, and afterwards subsisted largely on seaweed.

Meat from the North Ronaldsay has a distinctive flavour, described as "intense" and "gamey",[3] possibly in part due to the high iodine content in their diet of seaweed.

[7][8] They share some characteristics, including their colour range and short tails, with Scandinavian sheep introduced when the islands were under Norse control, between the 9th and 15th centuries.

Its construction was part of the response to the collapse of the kelping industry, which was the production of soda ash by the burning of seaweed.

To provide a livelihood for those previously employed in kelping, the inland farmlands were reorganized, and the sheep kept away from the fields or crofts.

[11][12][13][14] The wall also unintentionally reduced the chances of crossbreeding, which would have diluted the gene pool of an already vulnerable breed.

[20] In 2015, Orkney Islands Council reported that some 4.7 km (3 mi) of the wall was in need of work, and that the rate of damage exceeded that of repair.

[16] The punds, or pounds, also listed with Historic Scotland,[17] are nine small enclosures situated across the island to contain the sheep for shearing, counting, lambing and slaughtering.

This has evolved due to their unique location, confined to the shoreline by a 1.8 m (6 ft) dry stone wall, leaving only seaweed for food.

The other sheep (males and non-pregnant females) remain on the shore, primarily consuming seaweed, throughout the year.

[40] Unusually for sheep, the North Ronaldsay fattens in winter when storms throw larger amounts of kelp and seaweed onto the shore and food is abundant.

[22] A 2005 study at the University of Liverpool found that they have a greater susceptibility to copper toxicity, when compared with a more traditional breed such as the Cambridge.

[22] The levels of copper found in typical sheep feed, including grass, are toxic for this breed.

[31][46] Studies at the Universities of Liverpool and Minnesota suggest that they can extract four times more copper from their diet than more traditional breeds.

[53] The meat has a unique, rich flavour, which has been described as "intense and almost gamey",[3] and has a darker colour than most mutton, due in part to the animals' iodine-rich diet.

More common typical colours are the whites and greys, but browns, beiges, reds (also called tanay) and blacks, with coarser hair, are all exhibited.

[34] The undercoat tends to be finer and soft, suitable for garments that would touch the skin, whereas the overcoat is coarser, with long hair that protects the sheep from the cold, wet weather of their natural environment.