From June to September 2007, 27 occupied Leach’s Storm-petrel Oceanodroma leucorhoa burrows on St Kilda were investigated by endoscope to estimate phenology and breeding success. From 17 burrows that could be followed to chick development, a minimum productivity of 0.59 young per egg laid was estimated, similar to other published figures of breeding success from the northwest Atlantic. Similar life cycle timings to those of Leach’s Storm-petrels in the northwest Atlantic were revealed, with egg laying in late May to mid June, hatching in mid to late July and fledging from mid September onwards. Implications for conservation and monitoring are discussed, and guidance for future studies suggested.

The St Kilda archipelago (57°49’N, 08°35’W), 66 km west of the Western Isles, holds a population of around 45,000 pairs of Leach’s Storm-petrels Oceanodroma leucorhoa which represents 94% of the British and Irish population (Mitchell 2004). Recent work in the northwest Atlantic by Huntington et al. (1996) and A. Hedd (unpubl.) has been carried out on the breeding biology of Leach’s Storm-petrel, but little is known about their breeding habits within Britain, and little has been published since that of Ainslie & Atkinson (1937) on the Flannan Isles and North Rona, apart from some exploratory work on Gruney, Shetland in the 1990s (Ellis et al. 1998). In addition, it has been suggested that the Leach’s Storm-petrel breeding population on St Kilda may have declined significantly since the last full census in 1999/2000 (Mitchell 2004; Newson et al. 2008), and studies on breeding success may therefore give insights as to the reasons for this decline.

This work was supported by the National Trust for Scotland and the Joint Nature Conservation Committee, Aberdeen. We also thank Stuart Murray for encouraging this publication, April Hedd for allowing access to unpublished data, and two anonymous referees for improving an earlier draft of the manuscript.

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