Rats and cats are a serious problem where they are present; the large shearwater colony on the Calf of Man was destroyed by rats that arrived from a shipwreck in the late 18th century. European hedgehogs eat the eggs of nesting seabirds where they have been introduced. Red deer have been recorded killing and eating young shearwaters on at least Foula, Skokholm, and Rùm; on the latter island, 4% of the chicks are killed by deer, and sheep have also been involved. The reason for the carnivorous behaviour is thought to be a need for extra calcium.