An aerial survey of Northern Gannets Morus bassanus on Scar Rocks, southwest Scotland, in 2014

Stuart Murray1*, Mike P. Harris2 and Sarah Wanless2

1Easter Craigie Dhu, Dunkeld, Perthshire PH8 0EY, UK;

2Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian EH26 0QB, UK.

Full paper

Abstract

An aerial survey to assess the number of Northern Gannets Morus bassanus on Scar (Scare) Rocks, southwest Scotland in July 2014 indicated 2,376 apparently occupied sites. This was almost identical to the number recorded using the same method in 2004. Numbers at this colony have increased rapidly during the past 60 years but Northern Gannets now have little space to increase further and the colony may be full.

Introduction

The Scar (Scare) Rocks (54&°;4'N 4&°;42'W) sit in the entrance to Luce Bay, Dumfries and Galloway, 11 km east of the Mull of Galloway (Figure 1). Northern Gannets Morus bassanus nest on the largest rock in the group, Big Scar. Although less than 1 ha in extent and with a maximum height of only 25 m, Big Scar has all the features typical of an offshore island, but on a reduced scale. There is a vertical cliff face on the north side and an almost detached stack (Castle Rock) on the west side (Figure 2). The main part of the island slopes at a gentle angle seaward from the highest point, mainly towards the south and southeast. The low coastline offers no barrier to storm driven waves and in such conditions they can reach well up the slope and may prevent seabirds from nesting any closer to the sea than they presently do. The raised beds of eroded blue-grey schist have resulted in a rock surface of parallel dykes and trenches that results in some birds being invisible from the sea.

Northern Gannets (hereafter 'Gannets') were first recorded ashore on Scar Rocks (then known as Big Scaur) in 1883 when two nests were found, one of which contained a broken egg (Gurney 1913). There were no subsequent records of breeding until 1939 when a single nest with a chick was found (McWilliam 1939). Regular counts since have shown that the population has increased year-upon-year (Fisher & Vevers 1943; Young 1968; North Solway Ringing Group 1973; Nelson 2002). Most counts prior to 1984 were of nests made from the land, sometimes augmented by observations made from the sea. However, as the colony expanded movement by people on the rock was restricted to avoid disturbance and this made obtaining an accurate count difficult, since some parts of the colony could not be seen from the few accessible vantage points (P. N. Collin pers. comm.). An attempt was made at an aerial survey in 1994 but it proved impossible on the photographs to separate birds in clubs from nesting birds (P. N. Collin pers. comm.). Successful aerial surveys were undertaken in 1995 and 2004 during regular decadal assessment of the British and Irish populations (Murray & Wanless 1997; Wanless et al. 2005). This note reports on an aerial survey carried out in 2014.

Acknowledgements

Our thanks go to Dave Cowley who made the survey possible and to pilot Ronnie Cowan for carrying it out with maximum efficiency and at minimal expense. We also thank members of the North Solway Ringing Group and others who made earlier counts of this gannetry. The flight was largely funded by a grant from the Seabird Group to SW for which we are extremely grateful.

References

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McWilliam, J. M. 1939. Breeding of gannet on the Scar Rocks, Wigtownshire. British Birds33: 105–107.

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Wanless, S. & Harris, M. P. 2004. Northern Gannet Morus bassanus. In: Mitchell, P. I., Newton, S. F., Ratcliffe, N., & Dunn, T. E. (eds.) Seabird Populations of Britain and Ireland: 115–127. Poyser, London.

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