Atlas of Seabirds of Portugal

Distribution, movements and phenology

The Bulwer’s Petrel is pantropical, occurring in the three major oceans. It breeds in the Eastern Atlantic, between the Azores and Cape Verde, and in the Western Pacific, from Asia to Hawaii, including the Marquesas Islands (Billerman et al. 2026). The species makes extensive use of the Portuguese EEZ during the breeding season (April to October), occurring mainly in the open sea (Meirinho et al. 2014; Dias et al. 2016; Ventura et al. 2022). On the Mainland, it occurs mainly in summer and autumn, along the continental shelf, avoiding coastal areas (Catry et al. 2010a). Individual tracking data from 66 birds from Madeira (Deserta Grande and Selvagem) and the Canary Islands, fitted with GPS devices between 2010 and 2021, confirm this distribution, highlighting the central and south-eastern areas of the Azores and south of Madeira. During the non-breeding season, available tracking data obtained from individuals from Selvagem Grande, Vila Islet (Azores) and Montaña Clara (Canary Islands) indicate that the birds migrate southwards, heading towards deep equatorial ocean waters (Zino et al. 2012; Dias et al. 2015; Ramos et al. 2015b; Cruz-Flores et al. 2019).

Abundance and population trends

The global population has been estimated at around 500,000 to 1,000,000 mature individuals, with a stable trend (BirdLife International 2025). In Portugal, the majority of the population appears to be concentrated on the Desertas Islands, where 45,000 pairs have been estimated (Catry et al. 2015). There are no robust estimates for the rest of the Madeira archipelago, but it is likely that the Selvagens colony numbers several thousand pairs (Equipa Atlas 2022). In the Azores archipelago, it breeds on the islet of Vila (Santa Maria) with 65 breeding pairs, on the islet of Baixo (Graciosa) with 17 pairs (Pipa & Silva 2021; Pipa et al. 2024) and on the islet of Praia in very small numbers. Due to a lack of data, an assessment of environmental status was only possible for the Azores population, which shows an increase in both indicators — abundance and productivity — and has achieved Good Environmental Status.

Ecology and habitat

The Bulwer’s Petrel is a pelagic bird, approaching land only during the breeding season. Nests are located in excavated burrows, small rock cavities and piles of scree (Billerman et al. 2026). The diet consists mainly of mesopelagic fish and cephalopods (Zonfrillo 1986; Neves et al. 2011a; Waap et al. 2017), feeding primarily at night and taking advantage of the vertical migration of prey to the surface of the water column (Dias et al. 2015; Dias et al. 2016).

Threats and conservation

Predation by introduced species, such as brown rats, cats and mustelids, is the main threat to the species, and the Bulwer’s Petrel is therefore confined to islands and islets free of these predators. Adults and chicks are also preyed upon by Yellow-legged Gulls Larus michahellis (Matias & Catry 2010). In the Azores, the species competes directly with the Cory’s Shearwater Calonectris borealis due to a scarcity of suitable nesting habitat (Ramos et al. 1997; Bried & Bourgeois 2005), leading a significant proportion of breeding individuals to fail to breed every year (Cruz-Flores et al. 2021). Other threats include light pollution (Rodríguez et al. 2012), the ingestion of marine litter (Carvalho 2012) and mercury accumulation (Furtado et al. 2021). Furthermore, the rise in sea surface temperature caused by climate change may negatively affect the species’ survival (Cruz-Flores et al. 2022).