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Little Tern-designated Natura 2000 Sites Overlapped Just 0.18% of the Tracked Core Area in Cádiz

Little tern standing on a sandy shore in Bahía de Cádiz, Spain
Conservation · Management

GPS tracking of breeding little terns (Sternula albifrons) in the Bay of Cádiz, Spain, found a striking contrast in how well different parts of the Natura 2000 network matched the birds’ space use. Natura 2000 sites overall covered much of the area used most intensively by the tracked population, while sites specifically designated for little tern under the Birds Directive covered very little of it. The study was first available online on 21 June 2026 in Ocean & Coastal Management.

Researchers tracked 29 adults during incubation over two consecutive breeding seasons and collected more than 260,000 GPS positions. At population level, the broader home range — the area encompassing about 95% of the modelled space use — was estimated at 377.23 km². The core area, defined by the 50% utilisation contour and representing the most intensively used part of the range, covered 9.50 km².

Natura 2000 covered much of the core area overall

Across all Natura 2000 sites considered together, 37.9% of the population home range and 75.9% of the core area fell within the network. The study compared 22 Natura 2000 sites overlapping the study area: 11 designated for breeding birds including little tern, and 11 established for other species or habitats.

When the analysis was restricted to sites specifically designated for little tern, the corresponding coverage fell to about 2.0% of the broader home range and just 0.18% of the core area. The Bahía de Cádiz SPA/SAC ES0000140 was the only species-designated site containing a substantial part of the tracked distribution. Estrecho Occidental overlapped very little, and none of the tracked birds used the Doñana site during the study.

Sites designated for other targets sometimes matched the birds better

Some Natura 2000 sites established for other conservation targets aligned much more closely with the birds’ movements. Fondos Marinos de la Bahía de Cádiz, designated primarily for marine habitats such as submerged sandbanks and intertidal flats rather than specifically for little tern, overlapped almost entirely with the estimated population home range.

The authors argue that this mismatch partly reflects how protected areas were originally delineated. Many sites were designated before high-resolution GPS tracking was available, often around known breeding colonies or from broader census information. Little tern colonies are dynamic and can shift with vegetation growth, predation, disturbance and other changes, so fixed boundaries based on older colony locations may not continue to match the places birds use most intensively.

The tracking covered incubation during two breeding seasons, so it represents a defined time window rather than every possible year or breeding stage. The authors nevertheless conclude that high-resolution tracking can help future reviews of protected-area boundaries and management better reflect the functional space used by small, mobile coastal birds.

Sources and image credit

  1. De la Cruz, A., Korneeva, Y., Martín, N., Forján, A., Couso, M., Montesinos, J. M., Pérez-Hurtado, A., Castro, M., Álvarez, A., Pereira, J. M., Paiva, V. H., Ramos, J. A., Márquez-Rodríguez, A., Reyes-González, J. M., & Arroyo, G. M. (2026). Quality over quantity: Assessing Natura 2000 coverage of Little Tern core areas. Ocean & Coastal Management, 279, 108271. https://doi.org/10.1016/j.ocecoaman.2026.108271Primary research article. Available online 21 June 2026; GPS tracking of 29 adult little terns over two breeding seasons in the Bay of Cádiz.
  2. Universidad de Cádiz. (2026, August 26). La UCA identifica nuevas áreas prioritarias para mejorar la conservación del charrancito común.University research release summarising the study and confirming 29 tracked adults, more than 260,000 GPS positions and the conservation-planning context.

Image: Agustín Povedano / Wikimedia Commons / Flickr — little tern (Sternula albifrons) photographed in Bahía de Cádiz Natural Park, Spain, 28 July 2011; representative species image from the study area · CC BY 2.0 · Source

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