Nocturnal and diurnal nearshore foraging of European Storm Petrels Hydrobates sp. along the Lisbon coast, Portugal

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-During three days in June 2006, tens of European Storm-petrels Hydrobates sp. were observed foraging along the Lisbon coast during full daylight. On one morning along a 12 km stretch of coast between Guincho and Parede a minimum of 135 different birds were observed foraging up close to the rocky shores and inside the Estoril bay. In September 2007 birds were observed fl ying towards the coast of Guicho Bay and foraging close to the shore near Cabo Raso. In September almost all birds were seen in the evening after sunset. Up to a maximum of 97 different birds were observed in one evening. It is discussed that the patterns of occurrence of the Storm-petrels nearshore in both periods must be explained by a combination of high food availability and a lowered predation risk. The observations in September 2007 of birds actively foraging nearshore in the dark are in line with two diet studies, where it was concluded that Storm-petrels regularly use inshore and nearshore areas at night to forage, based on found prey species in regurgitates, with one of the studies made in the southwest of Portugal. The observations in June 2006 are a novelty as they show that relatively intense nearshore foraging can also occur during the day and does not have to be confi ned to the darkness of the night. The low risk of predation in June, compared to other periods of the year when large numbers of gulls and Greater Skuas Stercorarius skua are present, might play a role here as well, like in nocturnal foraging. Although the observations in both June and September coincide with the main migration period of northern breeding populations of European Storm-petrels, attention is drawn to the possibility that local breeding might occur along the Portuguese coast. Effort is needed to check for breeding birds on the isolated islands in front of the coast of Cabo da Roca, being the best potential breeding locations in the region.
Original languageEnglish
Pages (from-to)13-21
Publication statusPublished - Jan 2008
Externally publishedYes


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