Two gulls in
the Galician Coast

From the Mediterranean, to the Atlantic Coast of Galicia, with its rias, islands and treacherous cliffs: that is where the seabirds have led our team now.

The Sisargas are a small, rugged archipelago off the Costa da Morte, characterised by steep cliffs, limited human disturbance, and rich surrounding waters. This isolation makes them a key refuge for breeding seabirds, especially gulls and shags. Ons Island, part of the Parque Nacional Marítimo-Terrestre das Illas Atlánticas de Galicia, is larger and more accessible, with a mix of natural habitats and seasonal human presence. Despite this, it supports significant breeding populations of yellow-legged and lesser black-backed gulls, especially in its steeper, less disturbed areas. Both sites are recognised as Key Biodiversity Areas (KBAs) due to their role in supporting important seabird colonies, particularly for gulls and other species of conservation concern. Their protection is vital to maintaining healthy populations in the northeastern Atlantic.

In Galicia, these two gull species with similar habits but different conservation trends share the coastline: the Yellow-legged Gull (Larus michahellis) and the Lesser Black-backed Gull (Larus fuscus).

🔹  The yellow-legged gull is still the most abundant breeding gull in the region, nesting on cliffs, islets, and increasingly in urban environments. However, despite its apparent ubiquity, the population is declining across much of Galicia. The reasons are not fully understood, but may relate to changes in food availability (e.g. fishery discards, landfill access), breeding success, and urban pressures.

🔹The lesser black-backed gull is mostly known in Galicia as a wintering and migratory species, but in recent years it has also become a scarce breeder, with a few known nesting sites mainly in the north. The breeding population remains very small and localized, and is likely underestimated due to the difficulty of detecting mixed colonies and low densities.

The sampling took place in spring, from May to early June, coinciding with the peak of the gulls’ breeding season, when adults are most active around their nests and dependent chicks. Fieldwork was carried out in two important nesting areas for seabirds: the Sisargas Islands and Ons Island, both located along the Galician coast but representing different ecological contexts. The fieldwork on both islands was led by our collaborating researchers Víctor García Matarranz and Andreia Zuzana Ribeiro Días, from the General Directorate for Biodiversity, Forests and Desertification of the Ministry for the Ecological Transition and the Demographic Challenge. 

In total, 11 gulls of both species were equipped with solar-powered GPS–GSM devices from Ornitela, attached using a lightweight harness. These units transmitted location data in near real time, allowing researchers to closely follow the birds’ movements. The tracked individuals travelled long distances from their nesting areas, with movements mostly over marine environments. However, they also made frequent inland incursions, demonstrating their remarkable ecological flexibility and capacity to exploit a wide variety of marine and terrestrial resources.

As in previous fieldwork campaigns carried out in Alborán and the Canary Islands, this study in Galicia is part of a broader effort to use tracking data to better understand how seabirds interact with their environment—and how conservation measures can be improved accordingly. In Galicia, the analysis of the GPS tracks recorded during the spring campaign will shed new light on how gulls use marine and terrestrial habitats during the breeding season. This knowledge is crucial for identifying critical foraging areas, understanding exposure to human pressures, and ultimately contributing to the expansion and refinement of marine protected area networks, such as RAMPE and Natura 2000.

This work is supported by the PLEAMAR Programme of the Fundación Biodiversidad, under the Spanish Ministry for the Ecological Transition and the Demographic Challenge. The AMPLIAMAR project is also co-financed by the European Maritime, Fisheries and Aquaculture Fund (FEMPA) of the European Union.

These tracking efforts were carried out with the support of the project, funded by the Fundación Biodiversidad of the Ministry for the Ecological Transition and the Demographic Challenge (MITECO). We also thank the Xunta de Galicia and the Parque Nacional Marítimo-Terrestre de las Islas Atlánticas de Galicia for providing the permits and support that enabled fieldwork in Galicia.

Through targeted fieldwork and modern tracking technology, we aim to deliver science-based recommendations that strengthen marine conservation planning at a time when seabirds—and the ecosystems they depend on—face increasing threats.
Stay tuned for more updates as we continue to uncover the hidden journeys of seabirds along Spain’s coasts and beyond.