"The have survived for 50 years without interference by man and maintain high density on rich maritime pastures heavily manured by s. They are a obtained from a cross between old Scottish shortwool and early blackface sheep. There is a population of about 400 on about 55 of pasture and the rams and ewes (with lamb and yearling rams) run in separate groups. The survival of rams is poor compared with ewes with an adult sex-ratio of about 10 ewes to 1 ram. Numbers of sheep fluctuate between 330 and 460 without causing sheet erosion, landslipping and disruption of the vegetation. The conservation plan for Boreray rests on continued non-interference with the sheep and no sheep should be introduced to the island."