Barolo Shearwater

Distribution, movements and phenology

The Barolo Shearwater occurs in the tropical and temperate waters of the North Atlantic, breeding in the archipelagos of Macaronesia. In Portugal, it breeds on islands and islets in the Azores and Madeira archipelagos between December and June (Neves et al. 2012; Equipa Atlas 2022). After breeding, it does not undertake large-scale migrations (Neves et al. 2012; Paiva et al. 2016; Ramos et al. 2020), with at least part of the population remaining in the vicinity of the colonies and even visiting them during this period (Billerman et al. 2026). It occurs throughout the Portuguese EEZ, with the highest density in the Madeira sub-area (Meirinho et al. 2014). This occurrence was confirmed by individual tracking data from 27 birds fitted with GLS devices, originating from colonies in Madeira and the Azores, indicating extensive use of all sub-areas of the EEZ, both during the breeding and non-breeding periods. It appears to avoid only the very deep waters of the westernmost part of the Azores sub-area.

Abundance and population trends

In Portugal, the population has been estimated at between 2,407 and 5,578 pairs (Equipa Atlas 2022), which is thought to account for over 83% of the global population (BirdLife International 2025). In the Azores, the species nests on several islands and islets, although not all colonies have been confirmed and there is little information on population size and trends. For the period 1996–2004, the population was estimated at between 895 and 1,741 pairs (Monteiro et al. 1999; Equipa Atlas 2022). Between 2018 and 2022, 23 breeding pairs were estimated on Vila Islet and 17 pairs on Praia Islet (Pipa et al. 2024). In the Madeira archipelago, it occurs in small numbers on the islands of Madeira, Porto Santo and the Desertas Islands, being more abundant on the Selvagens Islands. In 2013, the breeding population on Selvagem Grande was estimated at 1,383 to 3,684 pairs and, on Cima Islet (Porto Santo), between 129 and 148 pairs (Isabel Fagundes pers. comm.). These figures, compared with the previous census on Selvagem Grande (Oliveira & Moniz 1995; Moniz et al. 1997), suggest a decrease of between 24.7% and 32.6% over 20 years. Nevertheless, the lack of a minimum time series made it impossible to assess the environmental status of the Madeira population. In the Azores, however, the breeding population did not achieve Good Environmental Status for the abundance indicator.

Ecology and habitat

The Barolo Shearwater is a non-migratory pelagic bird, but may disperse up to 2,500 km from its colonies (Neves et al. 2012). It nests in ground cavities and on inaccessible cliffs, and may share nesting areas with other seabirds. Its diet consists mainly of small cephalopods and fish, diving to an average depth of approximately 15 m (Monteiro et al. 1998; Neves et al. 2012; Ramos et al. 2015).

Threats and conservation

The main threats are predation by introduced mammals, reduction of nesting habitat, indigenous predators such as the Yellow-legged Gull Larus michahellis, light pollution and interspecific competition for nesting cavities (Monteiro et al. 1996a; Rodríguez et al. 2012). Climate change and severe weather events pose a growing threat, as the increased frequency and intensity of storms can cause changes to nesting habitat or flooding (Fagundes et al. 2016). Furthermore, climate change may alter oceanographic conditions, potentially leading to a decline in prey abundance (Ramos et al. 2015a).

Autores

Isabel Fagundes, Tânia Pipa, Zuzana Zajkova, Verónica Neves

Owners/sources of tracking data

Neves & Gonzalez-Solis 2008, Paiva 2013, Paiva 2014