Seabirds breeding at the Berlengas, forty‐two years after Lockley's visit

Changes in seabird numbers and distribution have been monitored in the British Isles for decades, contrasting sharply with the paucity of equivalent information available from some adjacent regions. This situation in the past encouraged several expeditions by British specialists to some of the Portuguese colonies. Long since recognized as a major seabird site in Iberia, the Berlengas were visited by R. M. Lockley, who stayed on the main island from 20 to 24 June 1939. At that time, only four seabird species were found breeding at Berlenga (Lockley 1952), namely Cory’s Shearwater Calonectris diomedea, Shag Phalacrocorax aristotelis (c.70 pairs), Herring Gull Larus argentatus (c.1000 pairs) and Guillemot Uria aalge (c.6000 pairs). Breeding of all four species had been known to earlier ornithologists (Daveau & Girard 1884, Paulino d’oliveira 1896, Lopes Vieira 1904, Tait 1924, Reis Junior 1931) though population sizes had not been estimated prior to Lockley’s visit. Unfortunately, it is not clear which census techniques Lockley used to make his evaluation of the breeding populations (Lockley 1952), and care must be taken when using his results to check any subsequent population changes. The Berlenga islands are located off the western coast of Portugal, near the fishing village of Peniche. This group includes Berlenga itself with some associated rocky stacks, the smaller Estelas and the Farilhoes. (Fig. 1). Geologically, both Berlenga and the Estelas are granitic whereas the Farilhoes are composed of gneiss. Permanent human settlements exist only at Berlenga and occupation fluctuates markedly during the year, reaching a peak in July and August due to the influx of tourists from the mainland. During the breeding seasons of 1977, 1978 and 1981, census work was carried out at the Berlengas, following current techniques described elsewhere (Cramp et al. 1974, Lloyd 1975, Nettleship 1976). A further three species were found to breed, namely Madeiran Petrel Oceanodroma castro, Lesser Black-backed Gull L. fuscus and Kittiwake Rissa tridactyla. Cory’s Shearwater still breeds at the Berlengas, in spite of much human persecution in past times (see Fisher & Lockley 1954). In 1981, as many as 550 Cory’s were counted in late July, ‘rafting’ at dusk between Berlenga and the Estelas and early in September of the same year, c.600 Cory’s were also counted ‘rafting’ close to the Farilh6es but the actual size of the breeding population is very difficult to census correctly. From the relatively small number of birds observed ashore at night and a