A review of the status of Great Northern Diver Gavia immer in Galicia, northwest Spain
https://doi.org/10.61350/sbj.23.76
* Correspondence author. Email: xerobert@udc.es
1 O Graxal 10, 1o dcha., E-15172 Oleiros, A Coruña, Spain
2 Faculty of Sciences, University of A Coruña, Campus da Zapateira s/n, E-15071 A Coruña, Spain
3 Terranova Interpretacíón y Gestión Ambiental S.L., Álvaro Cunqueiro 2, entresuelo centro, 15008 A Coruña, Spain
Abstract
The status of the Great Northern Diver Gavia immer in Galicia, northwest Spain, is reviewed. Numbers peaked in late autumn and early winter, and again in spring. Post-breeding moult was recorded from November to mid December. Individuals in flight feather moult were recorded between February and March, the rest of the pre-breeding moult extending until the last birds departed around mid May. It is suggested that new birds arrive in the area in early spring to moult, replacing part of the wintering population. The species showed a strong preference for exposed sandy coasts in all seasons, but particularly in late winter and spring. The wintering population declined markedly following the Prestige oil spill in 2002/03 (c. 57% from 2002 to 2005). After 2005 the population returned to previous levels, possibly through immigration of birds from the nearby region of Asturias, where the wintering population collapsed in the same period. The average wintering population (uncorrected for detectability) was 123 birds (95% CI = 76–166), c. 2.5% of the estimated European wintering population.
Introduction
Great Northern Divers Gavia immer are scarce winter visitors to Iberia (Díaz et al. 1996), where they prefer the shallow open coasts of the Cantabrian-Atlantic coasts of Spain (Paterson 1997). Until recently there had been no standardised monitoring of the species in these waters, and beyond some notes in regional bird reports, systematic counts were localised with little temporal coverage (Paterson 1997). The Iberian population was estimated to be at least 500 birds in the early 1990s (Álvarez Laó 1993), but with only 60–110 found in northwest Iberia (Paterson 1997). A more recent conservative estimate was of 270–340 individuals for Spain (Sandoval & De Souza 2005), while the species is still considered a rarity in Portugal (Matias et al. 2007; Anon. 2010).
Great Northern Divers are highly vulnerable to oil spills (Camphuysen 1989). On 19 November 2002 the tanker Prestige broke in two 240 km off the Galician coast, leaking 66,000 tonnes of oil that affected over 800 km of the northwest Spanish coastline (González et al. 2006). Although most of the 23,130 birds recorded on beached bird surveys during the incident were auks (Alcidae), 65 Great Northern Divers were found stranded between northern Portugal and southern France, mostly in Galicia (García et al. 2003).
Taking all this into account, there is a need for recent and accurate information on numbers, since Great Northern Diver is listed in the Red Book of Birds of Spain (Madroño et al. 2004). Here we review its status in Galicia, where most of the Iberian population is concentrated, providing information on phenology, population size and trends, and habitat preferences, with special attention paid to the effect of the Prestige oil spill.
Acknowledgements
This work was started by one of the authors (AB) as part of a broader study on seabird population estimates on the Galician waters organized by SEO/BirdLife with fundings from the Fundación Arao. All the contributors to the Annual Bird Reports are thanked since they made possible many of the data analyses. We are especially grateful to José M. Alonso Pumar, Mercedes Fresco, Ricardo Hevia, Manu Polo, Amadeo Pombo and Luis J. Salaverri for giving us access to data from their monitored sites. Miguel Lorenzo, from the Xunta de Galicia, made available the data from the Galician Waterfowl January Censuses from the period 1987–2007. Paco Girón, Antonio Gutiérrez, Pablo Gutiérrez, Antonio F. Marín, Xabi Prieto and Juan R. Silvar also informed us on the status of the species in northern Galicia. We thank Gabriel Pérez Villa for drawing the figures. Finally, we thank Martin Heubeck, Andy Webb and two anonymous referees for language improvements and helpful comments.
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