A survey of Leach’s Oceanodroma leucorhoa and European Storm-petrel Hydrobates pelagicus populations on North Rona and Sula Sgeir, Western Isles, Scotland

Leach’s Storm-petrel Oceanodroma leucorhoa was first recorded breeding on North Rona in 1883 and on Sula Sgeir in 1939. European Storm-petrel Hydrobates pelagicus was first recorded on North Rona in 1885 and on Sula Sgeir in 1958. Since then, there have been attempts to estimate the population size of both species on North Rona but there is little information about their current status on Sula Sgeir. In 2001, systematic surveys of both species using tape playback were conducted for the first time on both islands. North Rona held 1,133 Apparently Occupied Sites (AOS) of Leach’s Storm- petrel but only 371 AOS of European Storm-petrel; numbers on Sula Sgeir were five and eight AOS respectively. The combined population of both North Rona and Sula Sgeir of Leach’s Storm-petrel and European Storm-petrel, comprise 2.3% and 1.4% respectively, of the total number of each species breeding in Great Britain.