This study investigated whether increased numbers of Larus gulls on the English Channel Island of Burhou restrict or endanger the island’s Atlantic Puffin Fratercula arctica population. About 120 breeding pairs of Atlantic Puffins in 2005–07 indicated little change in numbers since 1980, although a large decline occurred between 1950 and 1980. Numbers of Great Black-backed Gulls Larus marinus have changed little since 1969 but their direct predation on the reduced population of Atlantic Puffins was a considerable addition to adult mortality rates. Kleptoparasitic attacks by a greatly increased population of Lesser Black-backed Gulls L. fuscus, and by Herring Gulls L. argentatus, were probably too infrequent and too unsuccessful to affect Atlantic Puffin breeding success. When a large Atlantic Puffin population is reduced, predation by Great Black-backed Gulls and reduced recruitment caused by high breeding densities of gulls may prevent recovery of that population.

The most southerly breeding populations of Atlantic Puffins Fratercula arctica in the east Atlantic, on Les Sept Iles (Brittany) and Burhou (Channel Islands), have been reduced from tens of thousands to 200–300 pairs over the last 60 years, the main declines having occurred by 1980 (Cramp et al. 1974; Danchin & Cordonnier 1980; Harris 1984; Lloyd et al. 1991).

Two likely factors contributing to this decline have been oil spills in the region and human disturbance. Oil spills from the grounding of the tankers Torrey Canyon in 1967 and Amoco Cadiz in 1978 were followed by substantial declines in the Atlantic Puffin (hereafter ‘Puffin’) population in Brittany (Pericaud 1979; Harris 1984), and it is likely that the Burhou population was similarly affected. More recently, oil spills from the tankers Erika off Brittany in 1999 (Cadiou et al. 2004) and Prestige off northwest Spain in 2002 (García et al. 2003) affected wintering seabirds in the Bay af Biscay, including Puffins. Human disturbance may also have contributed to the decline on Burhou, as between 1950 and the early 1980s fishermen and private individuals were permitted on the island at any time and a tourist boat landed daily during the breeding season (Pierce et al. 1986; Carney et al. 1999). A prohibition on visitors to the island during the Puffin breeding season was introduced in the mid 1980s and although the population has not declined any further (Mitchell et al. 2004) it shows no signs of recovery.

The failure of the Burhou Puffin colony to recover between 1980 and 2000, when many in the UK were increasing (Harris & Wanless 2004), suggests factors other than oil and disturbance may now be limiting numbers there, perhaps including climatic effects on food supply (Harris et al. 2005; Sandvik et al. 2005). However, the quality and quantity of the fish loads carried by Burhou Puffins in 2007 were at least as good as those seen at other UK Puffin colonies in recent years (M. Harris & S. Wanless pers. comm.), and a separate study on Burhou in 2006 and 2007 found Puffins carried mainly Gadidae and sandeels (Ammodytidae) of good-sized loads, indicating food supply during the breeding season was not then an issue (Sanders 2008).

Another factor that could be preventing any recovery of Burhou’s Puffins is the increased population of nesting gulls. Between 1969 and 2000 breeding numbers of Lesser Black-backed Gulls Larus fuscus in the Channel Islands rose dramatically, with smaller increases reported for Herring Gulls L. argentatus and Great Black-backed Gulls L. marinus (Mitchell et al. 2004). Gulls can kill Puffins and steal their food (Taylor 1985; Russell & Montevecchi 1996; Finney et al. 2001; St Clair et al. 2001). Kleptoparasitism may affect Puffin breeding success and chick survival directly, or indirectly by increasing energetic costs to adults undertaking avoidance and escape behaviours (Rice 1987), while the presence of large numbers of gulls at a Puffin colony can reduce recruitment (Finney et al. 2003). Here we examine the effects Larus gulls may have in preventing the recovery of Burhou’s Puffin population.

We thank the States of Alderney and the RSPB for financial support for the project. The monitoring and research work on Burhou would not have been possible without additional scientific input from Professor Mike Harris, Professor Sarah Wanless, Jamie Hooper (La Société Guernesiaise), the Guernsey ringers, in particular Paul and Catherine Veron and Ian Buxton, and the vast amount of practical help from Roland Gauvain and volunteers from the Alderney Wildlife Trust, in particular Bill Black, Tim Finding, Lindsay Pyne and Mark Wordsworth. Thanks also to all the local boat skippers and the Alderney Harbour Office for the time and effort they have devoted to the project and to the former warden of Burhou, the late John Dupont. We also thank Dr. Jonathan Green for his constructive comments on the manuscript.

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