Around 7,500 pairs of Northern Gannets Morus bassanus nest at two long- established gannetries off Alderney, Channel Islands, the second and third most southerly colonies in the world. This paper describes the temporal and spatial distri- bution within five geographic zones of recoveries of birds ringed as chicks at these colonies. First-year birds migrate south in autumn earlier than those from gannetries further north, many to waters off northwest Africa and some as far south as Senegal, while others move into Mediterranean Waters, perhaps more readily than juveniles from more northern colonies. Some remain in southern latitudes during their second summer but most have returned at least into West European Waters. After their second winter, immature birds tend to summer in Northern Waters, with recoveries often in the vicinity of different gannetries. Most Channel Islands birds probably recruit into their natal colonies, but some have recruited into more recently established gannetries, on Helgoland, Germany and Gjesvær, Finnmark, Norway. Recoveries of adults were mainly from Northern Waters, but also along the coasts of the Bay of Biscay and Atlantic Iberia, at all times of year.

There are two Northern Gannet Morus bassanus colonies in the Channel Islands, of which Les Etacs (Garden Rocks) is the larger, consisting of two groups of igneous rocks some 0.6 ha in extent (49o42’N 2o15’W). However, it was the smaller Alderney Sandstone stack of Ortac (0.12 ha) (49o43’N 2o15’W) that was colonised first in 1940. Counting during the Occupation of the Second World War was not possible, but by 1946 the gannetries were estimated to hold c. 450 pairs (Ortac c. 250, Les Etacs c. 200) (Dobson & Lockley 1946). Counts using aerial photography found that the colonies contained a minimum of 4,387 Apparently Occupied Sites (AOS) in 1984 (Ortac 2,062, Les Etacs 2,325) (Hill 1989), and 7,409 AOS in 2005 (Ortac 2,547 AOS, Les Etacs 4,862 AOS) (Sanders & Harris 2005), an average rate of increase of 3.3% per annum over the past 55 years. This compares with an average world population growth over the past 60 years of 2% per annum (Wanless et al. 2005). It is interesting, however, to also compare this growth rate with that on Rouzic, Sept-Îles, Brittany, France, the nearest gannetry to Alderney, which was established in the 1930s and grew by an average of 8% per annum from 1939 to reach 17,000 pairs in 2005 (Siorat 2004; Grémillet et al. 2006).

This paper describes the dispersal and migration of Northern Gannets (hereafter ‘Gannets’) born in the two Alderney colonies, and compares ring recovery data with that of other gannetries from further north, in relation to age, season and geographical area. Other published studies (Thomson 1939, 1974; Nelson 2002) have principally used data from birds ringed on the Bass Rock in the Firth of Forth, Ailsa Craig in the Firth of Clyde (both Scotland), Grassholm in the Irish Sea, and more recently established colonies in Norway (Barrett 1988). Comparisons are also drawn with an earlier study of Gannets from the Channel Islands colonies (Veron 1988).

We are indebted to Margaret Austin for the copy of the Gannet recovery database, and for her meticulous administration of the Channel Islands Ringing Scheme. Thanks also to Carole Kinnersly and Catherine Veron for inputting data. We are also grateful to all ringers over the past 60 years who have visited the gannetries. The States of Alderney kindly granted permission for these ringing trips, and over the years some highly skilled boatmen have landed us on the rocks, principally in recent decades Francis Herivel (retired) and Richard Keen. Finally we thank Sarah Wanless, Stephen Votier and David Grémillet and two anonymous referees for their constructive comments on earlier drafts of this paper.

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