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The project, carried out within the framework of the monitoring of the migration of glider, marine and coastal birds and passerines through the Strait of Gibraltar (Migres Programme), has carried out the assessment of the populations of two threatened seabirds through censuses from the coast during their migration: the Balearic shearwater (Puffinus mauretanicus) and the Cory’s shearwater (Calonectris diomedea). This information, according to the Migres Foundation, is essential to estimate the status and population trends of these two species, and is also useful for the designation of a Special Protection Area for Birds in the Strait of Gibraltar.

The overall objective of the project has been to assess the status and population trends of two threatened seabird species, the Balearic shearwater and the Cory’s shearwater.

The specific objectives were as follows:

• Conduct a coastal census of migratory populations of endangered shearwaters.
• Analyze the status and evaluation of population trends.
• Disseminate the results obtained.

• Planning of the censuses and the volunteer program and development of the daily censuses of seabirds from the coast. In total, 52 monitoring days were carried out during the period of maximum passage of shearwater species from the Punta Marroquí observatory (Isla de las Palomas, Tarifa).
• Analysis of the information collected in the census and preparation of the report of results.
• Dissemination of results at different scales depending on the target audience (general public, technicians and scientists).

The “Shearwaters of the Strait” project, carried out within the framework of the actions of the Migres Programme initiated in 1997, has been aimed at estimating the passage and trends of two species of threatened seabirds, the Balearic shearwater (Puffinus mauretanicus) and the Cory’s shearwater (Calonectris diomedea), based on the censuses of their migratory passage through the Strait of Gibraltar.

Thus, during the campaign, daily censuses have been carried out from the observatory of Punta Marroquí (Isla de las Palomas in Tarifa) by a team of expert ornithologists supported by volunteers. As a result, 323,348 seabirds belonging to 45 species have been recorded, the most abundant being the Cory’s shearwater, the Atlantic gannet, the Balearic shearwater and the black-footed tern.

Regarding the species studied in this research, it has been estimated that 17,000 Balearic shearwaters are passing through the Mediterranean and 301,570 Cory’s shearwaters are crossing towards the Atlantic, which shows, according to the Migres Foundation, the importance of the Strait of Gibraltar for the migration of these two threatened seabirds. In addition, according to the entity, it provides useful information for its possible designation as a Special Protection Area for Birds (SPA), within the framework of the project
LIFE INTEMARES
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