Atlas of Seabirds of Portugal

Distribution, movements and phenology

The Black-legged Kittiwake breeds from April to August in the Northern Hemisphere, in the temperate and Arctic coastal zones of the Atlantic and Pacific. Atlantic populations winter throughout the North Atlantic as far south as the Sargasso Sea and the West coast of Africa, including the entire Portuguese EEZ (Billerman et al. 2026). Birds wintering in our waters mainly originate from colonies in Norway, the United Kingdom and Iceland (Catry et al. 2010a), with some birds coming from Canada, the Faroe Islands, Greenland and Russia. It occurs regularly in the Azores and Madeira, although it is less abundant in the latter archipelago (Meirinho et al. 2014).
Individual tracking data for 368 birds from the colonies mentioned above confirm the extensive use of the Portuguese EEZ across its three sub-areas, with the highest concentration in the Mainland region, followed by the Azores and Madeira. The majority of the birds used these areas during their wintering period, between October and March.

Abundance and population trends

The global population has been estimated at 14.6 to 15.7 million individuals, of which 3,460,000 to 4,410,000 mature individuals occur in Europe (BirdLife International 2025). This population has declined sharply since the 1980s by >40% over three generations.

The species nested in Portugal, in the Berlengas archipelago, between the late 1970s and early 1980s, as a result of a natural expansion that led to the colonisation of other areas along the Iberian coast (Catry et al. 2010a). The size of the wintering population in Portuguese waters is very poorly documented, but appears to be related to weather conditions in more northerly regions and on the open sea. Based on the data used for the environmental status assessment, an estimate of between 3,100 and 10,700 individuals was obtained for the continental shelf in 2024. Despite the lack of more concrete estimates, this population appears to be in Good Environmental Status for the abundance indicator. There is no information on abundance or population trends for the Azores and Madeira.

Ecology and habitat

The Black-legged Kittiwake is a migratory bird that leaves the colonies after breeding, dispersing to the open sea from July and August (Olsen & Larsson 2004). It is mostly observed at sea, either alone or in small groups (Snow & Perrins 1998), and may congregate in productive areas such as continental shelves, upwelling zones and fish shoals. Its diet consists mainly of fish and marine invertebrates (including plankton), but it also feeds on discards from fishing vessels (Billerman et al. 2026).

Threats and conservation

Black-legged Kittiwake populations have been affected by reduced prey availability in the Atlantic, primarily due to climate change and, in part, to targeted industrial fishing (Frederiksen et al. 2012). Increased foraging effort and nutritional stress result in higher mortality and breeding failure (Paredes et al. 2014). The species suffers bycatch in longline fisheries, particularly in the Gran Sol bank, although the impact is low in other areas of the North Atlantic (BirdLife International 2025). Oil pollution contributes to a decline in the physical condition of adults and reduced breeding success (Nikolaeva et al. 2006). The species may also be vulnerable to outbreaks of avian influenza.