Atlas of Seabirds of Portugal

Distribution, movements and phenology

The Great Shearwater breeds in the South Atlantic, on the Tristan da Cunha archipelago, and in the Falkland Islands between mid-September and late May (Cuthbert 2005; Billerman et al. 2026). After breeding, it begins a long migration across the North-west Atlantic, reaching the coast of Canada, before heading eastwards, passing through the waters of the United Kingdom and the Iberian Peninsula (Billerman et al. 2026). In Portugal, it occurs throughout almost the entire EEZ during summer and autumn, being closer to the coast in summer and further out to sea in autumn (Meirinho et al. 2014), when it heads south towards its breeding grounds (Catry et al. 2010a; Billerman et al. 2026). Based on data from 44 birds fitted with GLS between 2009 and 2014 from colonies on Gough Island, greater use of the Portuguese EEZ was observed throughout September, although some birds used these waters as early as June. Their movements were concentrated mainly in the Azores sub-area and the north-west region of Madeira. On the Mainland, however, records were scarce, despite the species being known to occur frequently, with considerable concentrations along the southern coast (Araújo et al. 2022a).

Abundance and population trends

The global population was estimated at over 10 million mature individuals in 2004 (Brooke 2004). No estimates have been made since then, although the population is thought to be stable (BirdLife International 2025).
In Mainland Portugal, the population was estimated at between 5,399 and 25,379 individuals for the period between 2012 and 2015 (Araújo et al. 2022a). Despite significant interannual variations, an upward trend has been observed since 2015, reflected in the population abundance indicator, which justifies the population’s Good Environmental Status. In the case of the Azores and Madeira, however, the available information does not allow for firm conclusions to be drawn regarding the species’ population trends.

Ecology and habitat

During its wintering period, the Great Shearwater uses both coastal waters and those further offshore, preferring the latter during its pre-breeding migration. This essentially pelagic bird feeds mainly on fish, cephalopods, and crustaceans, caught at the surface or while diving (Billerman et al. 2026). It frequently feeds on discards from commercial fishing, mainly following trawlers (Paz et al. 2018), but also vessels using other fishing gear, notably gillnets and longliners (Bugoni et al. 2008; Pereira et al. 2025a).

Threats and conservation

In its breeding areas, the Great Shearwater is still caught for food (BirdLife International 2025). At sea, the greatest threat relates to bycatch in fishing gear operated in the North-east Atlantic, primarily longlines, trawls and gillnets (Perez & Wahrlich 2005; Bugoni et al. 2008; Hatch et al. 2016; Paz et al. 2018), the latter being a threat also reported in Mainland Portugal (Pereira et al. 2025a). Other causes of mortality may be related to heavy metal contamination and the ingestion of plastics (Pierce et al. 2004; Barbieri et al. 2007).