Volume 50, No. 1

Search by author or title:

Seabird abundance and distribution off western Iberian waters estimated through aerial surveys


1Sociedade Portuguesa de Vida Selvagem, Estação de Campo de Quiaios, 3081-101 Figueira da Foz, Portugal (
2Escola Superior de Educação do Politécnico do Porto, 4200-465 Porto, Portugal
3ECOMARE, Universidade de Aveiro, Estrada do Porto de Pesca, 3830-565 Gafanha da Nazaré, Portugal
4Department of Biology & CESAM Universidade de Aveiro, 3810-193 Aveiro, Portugal
5Coordinadora para o Estudio dos Mamíferos Mariños (CEMMA), Apdo, 156-36380 Gondomar, Spain


ARAÚJO, H., CORREIA-RODRIGUES, P., BASTOS-SANTOS, J., FERREIRA, M., PEREIRA A.T., MARTINEZ-CEDEIRA, J., VINGADA, J. & EIRA, C. 2022. Seabird abundance and distribution off western Iberian waters estimated through aerial surveys. Marine Ornithology 50: 71 - 80

Received 15 July 2021, accepted 13 January 2022

Date Published: 2022/04/15
Date Online: 2022/03/23
Key words: aerial surveys, distance sampling, Galicia, marine birds, MSFD, Portugal, Spain


Western Iberian waters are important migratory flyways, stopover sites, and wintering areas for several of the world's seabird species. To describe seabird species composition, distribution, and abundance in these waters, we performed six aerial surveys in September and/or October of each year, 2010-2015, covering 74 840 km2. Using line transect methodology, 27 396 seabird sightings from 17 taxonomic groups were recorded along 10 496.3 nautical miles (19 433 km). Using the program “Distance,” annual and overall abundance estimates were obtained for nine taxonomic groups: Balearic Shearwater Puffinus mauretanicus, Great Shearwater Ardenna gravis, Cory's Shearwater Calonectris borealis, shearwaters, Northern Gannet Morus bassanus, Sabine's Gull Xema sabini, Great Skua Stercorarius skua, storm petrels, and Red Phalarope Phalaropus fulicarius. For the six-year period, Northern Gannet was the most abundant species (89 630 individuals, coefficient of variation [CV] = 6.28%), followed by Cory's Shearwater (25 044 individuals, CV = 7.56%) and Balearic Shearwater (13 632 individuals, CV = 20.81%). The remaining taxonomic groups exhibited variable abundances. Results confirm that the study area is important to several seabird species, providing baseline estimates to inform conservation policies and instruments, such as the Birds Directive or the Marine Strategy Framework Directive.


ARAÚJO, H., BASTOS-SANTOS, J., RODRIGUES, P.C. ET AL. 2017. The importance of Portuguese Continental Shelf Waters to Balearic Shearwaters revealed by aerial census. Marine Biology 164: 1-14.

ARCOS, J.M., BÉCARES, J., RODRÍGUEZ, B. & RUIZ, A. 2009. Áreas Importantes para la Conservación de las Aves marinas en España. LIFE04NAT/ES/000049. Madrid, Spain: Sociedad Española de Ornitología (SEO/BirdLife).

ARROYO, G.M., MATEOS- RODRÍGUEZ, M., MUÑOZ, A.R., DE LA CRUZ, A., CUENCA, D. & ONRUBIA, A. 2014. New population estimates of a critically endangered species, the Balearic Shearwater Puffinus mauretanicus, based on coastal migration counts. Bird Conservation International 26: 87-99.

BAÑÓN, R., VILLEGAS-RÍOS, D., SERRANO, A., MUCIENTES, G. & ARRONTE, J. 2011. Marine fishes from Galicia (NW Spain): An updated checklist. Zootaxa 35: 262-264

BIRDLIFE INTERNATIONAL. 2018a. Puffinus mauretanicus. The IUCN Red List of Threatened Species 2018: e.T22728432A132658315. [Accessed at on 16 January 2021.]

BIRDLIFE INTERNATIONAL. 2018b. Morus bassanus. The IUCN Red List of Threatened Species 2018: e.T22696657A132587285. [Accessed at 2018-2.RLTS.T22696657A132587285.en on 18 January 2021.]

BIRDLIFE INTERNATIONAL. 2021a. Species factsheet: Calonectris borealis. Cambridge, UK: Birdlife International. [Accessed at on 18 January 2021.]

BIRDLIFE INTERNATIONAL. 2021b. Species factsheet: Catharacta skua. Cambridge, UK: Birdlife International. [Accessed at on 12 March 2021.]

BIRDLIFE INTERNATIONAL. 2021c. Species factsheet: Phalaropus fulicarius. Cambridge, UK: Birdlife International. [Accessed at on 18 January 2021.]

BOLDUC, F. & FIFIELD, D.A. 2017. Seabirds At-Sea Surveys: The Line-Transect Method Outperforms the Point-Transect Alternative. The Open Ornithology Journal 10: 42-52.

BRETAGNOLLE, V., CERTAIN, G., HOUTE, S. & MÉTAIS, M. 2004. Distribution maps and minimum abundance estimates for wintering auks in the Bay of Biscay, based on aerial surveys. Aquatic Living Resources 17: 353-360.

BROOKE, M.D.L. 2004. Albatrosses and Petrels Across the World. Oxford, UK: Oxford University Press.

BROWN, J.M., LOON, E.E., BOUTEN, W. ET AL. 2021. Long-distance migrants vary migratory behaviour as much as short-distance migrants: An individual-level comparison from a seabird species with diverse migration strategies. Journal of Animal Ecology 2021 90: 1058-1070.

BUCKLAND, S.T., ANDERSON, D.R., BURNHAM, K.P., LAAKE, J.L., BORCHERS, D.L. & THOMAS, L. 2001. Introduction to distance sampling: estimating abundance of biological populations. London, UK: Oxford University Press.

BUCKLAND, S.T., BURT, L.M., REXSTAD E.A., MELLOR, M., WILLIAMS, A.E. & WOODWARD, R. 2012. Aerial surveys of seabirds: the advent of digital methods. Journal Applied Ecology 49: 960-967.

CAMPHUYSEN, C.J., FOX, A.D., LEOPOLD, M.F. & PETERSON, I.K. 2004. Towards standardised seabirds at sea census techniques in connection with environmental impact assessments for offshore wind farms in the UK. Report No. BAM-02-2002. London, UK: COWRIE.

CATRY, P., COSTA, H., ELIAS, G. & MATIAS, R. 2010. Aves de Portugal, Ornitologia do Território Continental. Lisbon, Portugal: Assírio e Alvim

CERTAIN, G. & BRETAGNOLLE, V. 2008. Monitoring seabirds population in marine ecosystem: the use of strip-transect aerial surveys. Remote Sensing of Environment 112: 3314-3322.

DE JUANA, E. & GARCIA, E. 2015. The Birds of the Iberian Peninsula. London, UK: Christopher Helm.

DEAN, B.J., WEBB, A., MCSORLEY, C.A. & REID, J.B. 2003. Aerial surveys of UK inshore areas for wintering seaduck, divers and grebes: 2000/01 and 2001/02. JNCC Report, No. 333. London, UK: Joint Nature Conservation Committee.

DEL HOYO, J., ELLIOT, A. & SARGATAL, J. 1992. Handbook of the birds of the world, vol. 1: Ostrich to Ducks. Barcelona, Spain: Lynx Edicions.

DEL HOYO, J., ELLIOT, A. & SARGATAL, J. 1996. Handbook of the birds of the world, vol. 3. Barcelona, Spain: Lynx Edicions.

DERHÉ, M. 2012. Developing a Population Assessment for Scopoli's and Cory's Shearwaters Calonectris diomedea/Calonectris borealis. In: YÉSOU, P., BACCETTI, N., SULTANA, J. (Eds.) Ecology and Conservation of Mediterranean Seabirds and other bird species under the Barcelona Convention - Proceedings of the 13th Medmaravis Pan-Mediterranean Symposium. Alghero (Sardinia) 14-17 Oct. 2011, pp. 29-38. Alghero, Italy: Medmaravis.

DIAS, M.P., MARTIN, R., PEARMAIN, E.J. ET AL. 2019. Threats to seabirds: A global assessment. Biological Conservation 237: 525-537.

FERREIRA CORDEIRO, N.G., DUBERT, J., NOLASCO, R. & DESMOND BARTON, E. 2018. Transient response of the Northwestern Iberian upwelling regime. PloS One 13: e0197627.

FIFIELD, D.A., MONTEVECCHI, W.A., GARTHE, S., ROBERTSON, G.J., KUBETZKI, U. & RAIL, J.F. 2014. Migratory tactics and wintering areas of northern gannets (Morus bassanus) breeding in North America. Ornithologyical Monographs 79: 1-63.

GARTHE, S. 2019. Counting seabirds from ships and aircraft. [Accessed at on 04 February 2021.]

GARTHE, S. & HÜPPOP, O. 2004. Scaling possible adverse effects of marine wind farms on seabirds: developing and applying a vulnerability index. Journal of Applied Ecology 41: 724-734.

GRANADEIRO, J.P., DIAS, M.P., REBELO, R., SANTOS, C.D. & CATRY, P. 2006. Numbers and population trends of Cory's Shearwater Calonectris diomedea at Selvagem Grande, Northeast Atlantic. Waterbirds 29: 56-60.

GRÉMILLET, D., PONCHON, A., PALECZNY, M., PALOMARES, M.L.D., KARPOUZI, V. & PAULY, D. 2018. Persisting worldwide seabird-fishery competition despite seabird community decline. Current Biology 28: 4009-4013.

GRÉMILLET, D., PÉRON, C., PROVOST, P. & LESCROËL, A . (2015). Adult and juvenile European seabirds at risk from marine plundering off West Africa. Biological Conservation 182: 143-147.

GUILFORD, T., WYNN, R., McCMINN, M. ET AL. 2012. Geolocators reveal migration and pre-breeding behaviour of the critically endangered Balearic Shearwater Puffinus mauretanicus. PLoS One 7: e33753.

HAGEN, C. & WANLESS, R.M. 2014. Potential impacts of marine fisheries on migratory seabirds within the Afrotropical region. Unpublished report to the African-Eurasian Waterbird Agreement.

ICNF. 2014. Proposta técnica de Zonas de Protecção Especial no meio marinho a designar em Portugal continental. Lisbon, Portugal: ICNF. [Accessed at on 05 February 2016.]

JOINT, I., GROOM, S.B., WOLLAST, R. ET AL. 2002. The response of phytoplankton production to periodic upwelling and relaxation events at the Iberian shelf break: Estimates by the 14C method and by satellite remote sensing. Journal of Marine Systems 32: 219-238.

JONES, A.R., WYNN, R.B., YÉSOU, P. ET AL. 2014. Using integrated land- and boat-based surveys to inform conservation of the Critically Endangered Balearic shearwater. Endangered Species Research 25: 1-18.

KUBETZKI, U., GARTHE, S., FIFIELD, D., MENDEL, B. & FURNESS, R.W. 2009. Individual migratory schedules and wintering areas of northern gannets. Marine Ecology Progress Series 391: 257-265.

LEWISON, R., ORO, D., GODLEY, B. ET AL. 2012. Research priorities for seabirds: improving seabird conservation and management in the 21st century. Endangered Species Research 17: 93-121.

MACLEAN, I.M.D., SKOV, H., REHFISCH, M.M. & PIPER, W. 2006. Use of aerial surveys to detect bird displacement by offshore windfarms. BTO Research Report No. 446 to COWRIE. BTO. Thetford, UK: COWRIE.

MAGNUSDOTTIR, E., LEAT, H.K.E., BOURGEON, S. ET AL. 2012. Wintering areas of Great Skuas Stercorarius skua breeding in Scotland, Iceland and Norway. Bird Study 59: 1-9.

MARSH, H. & SINCLAIR, D.F. 1989. Correcting for visibility bias in strip transect aerial surveys of aquatic fauna. Journal of Wildlife Management 53: 1017-1024.

MARTÍN, B., ONRUBIA, A. & FERRER, M. 2019. Endemic shearwaters are increasing in the Mediterranean in relation to factors that are closely related to human activities. Global Ecology and Conservation 20: e00740.

MEIRINHO, A., BARROS, N., OLIVEIRA, N. ET AL. 2014. Atlas das Aves Marinhas de Portugal. Lisbon, Portugal: Sociedade Portuguesa para o Estudo das Aves..

MERKEL, F.R., JOHANSEN, K.L., DUE NIELSEN, R., PETERSON, I.K., STERUP, J. & MOSBECH, A. 2019. Wintering seabirds in south-west Greenland, 2017. Polar Research 38: 3462.

MOORE, C.C. 1994. Transect counts of pelagic seabirds in Azorean waters. Arquipélago: Life and Marine Sciences 12: 111-116.

MOURIÑO, J., ARCOS F., SALVADORES, R., SANDOVAL, A. & VIDAL, C. 2003. Status of the Balearic shearwater (Puffinus mauretanicus) on the Galician coast (NW Iberian Peninsula). Scientia Marina 62: 135-142.

MUNILLA, I., VELANDO, A. & GENOVART, M. 2015. Procesos de colonización y agregación social en la pardela cenicienta (Calonectris diomedea) en Galicia. Proyectos de investigación en parques nacionales: 2010-2013. [Accessed at on 31 March 2016.]

NICOLAU, L., MARÇALO, A., FERREIRA, M., SEQUEIRA, M., VINGADA, J. & EIRA, C. 2014. Sea turtles in Iberian waters: records from continental Portugal and Galicia. Proceedings of XIII Iberian Congress of Herpetology. 30th September-04th October 2014. Aveiro, Portugal: University of Aveiro.

NOER, H., CHRISTENSEN, T.K., CLAUSAGER, I. & PETERSON, I.K. 2000. Effects on birds of an offshore wind park at Horns. Rev: Environmental impact assessment. NERI report 2000. Aarhus, Denmark: National Environmental Research Institute of Denmark.

OLIVEIRA, N., ABREU, P., BORES, J., FAGUNDES, A.I., ALONSO, H. & ANDRADE, J. 2020. Evaluating the potential of artificial nests as a conservation measure for Cory's Shearwaters Calonectris borealis breeding in Berlengas Archipelago, Portugal. Airo 27: 3-19.

OLIVEIRA, N., HENRIQUES, A., MIODONSKI, J. ET AL. 2015. Seabird bycatch in Portuguese mainland coastal fisheries: An assessment through on-board observations and fishermen interviews. Global Ecology and Conservation 3: 51-61.

OPPEL, S., MEIRINHO, A., RAMÍREZ, I. ET AL. 2012. Comparison of five modelling techniques to predict the spatial distribution and abundance of seabirds. Biological Conservation 156: 94-104.

ORO, D. & MARTÍNEZ-ABRAÍN, A. 2004. Ecology and behaviour of seabirds. In: Duarte, C.M. (Ed.). The Encyclopedia of Life Support Systems (EOLSS). Oxford, UK: Eolss Publishers UNESCO.

OSPAR COMMISSION. 2016. Common Indicator: Marine Bird Abundance (B1), p. 1-26. (OSPAR Agreement 2016-09). OSPAR CEMP Guidelines. London, UK: OSPAR. [Accessed at on 29 January 2021.]

PANIGADA, S., LAURIANO, G., BURT, L., PIERANTONIO, N. & DONOVAN, G. 2011. Monitoring winter and summer abundance of Cetaceans in the Pelagos sanctuary (Northwestern Mediterranean Sea) through aerial surveys. PLoS One 6: e22878.

PARTNERS IN FLIGHT. 2020. Population Estimates Database, version 3.1. Brighton, USA: Birds Conservancy of the Rockies. [Accessed at on 04 March 2021.]

PERKINS, S., SADOTI, G., ALLISON, T., JEDREY, E. & JONES, A. 2005. Relative waterfowl abundance within Nantucket Sound, Massachusetts during the 2004-2005 winter season. Lincoln, USA: Massachusetts Audubon Society Technical Report.

PÉRON, C., GRÉMILLET, D., PRUDOR, A. ET AL. 2013. Importance of coastal marine protected areas for the conservation of pelagic seabirds: the case of Vulnerable yelkouan shearwaters in the Mediterranean Sea. Biological Conservation 168: 210-221.

PETTEX, E., DAVID, L., AUTHIER, M. ET AL. 2017. Using large scale surveys to investigate seasonal variations in seabird distribution and abundance. Deep Sea Research Part II: The Bay of Biscay and the English Channel. Deep-Sea Research Part II: Topical Studies in Oceanography 141: 74-85.

POOT, M. & FLAMANT, R. 2006. Numbers, behavior and origin of Mediterranean gulls Larus melanocephalus wintering along the west coast of southern Portugal. Airo 16: 13-22.

RAMÍREZ, I., GERALDES, P., MERINHO, A., AMORIM, P. & PAIVA, V. 2008. Áreas Marinhas Importantes para as Aves em Portugal. Projecto LIFE04NAT/PT/000213. Lisbon, Portugal: Sociedade Portuguesa Para o Estudo das Aves.

RIDGEWAY, M.S. 2010. Line transect distance sampling in aerial surveys for double-crested cormorants in coastal regions of Lake Huron. Journal of Great Lakes Research 36: 403-410.

RONCINI, R.A. & BURGER, A.E. (2009). Estimating seabird densities from vessel transects: distance sampling and implications for strip transects. Aquatic Biology 4: 297-309.

ROSSI, V., GARÇON, V., TASSEL, J. ET AL. 2013. Cross-shelf variability in the Iberian Peninsula Upwelling System: Impact of a mesoscale filament. Continental Shelf Research 59: 97-114.

SANTOS, J., ARAÚJO, H., FERREIRA, M. ET AL. 2011. Aerial survey of cetaceans along the Portuguese Northern Coast. European Cetacean Society Congress. 19th-23rd March 2011. Cádiz, Spain: European Cetacean Society.

THOMAS, L., BUCKLAND, S.T., REXSTAD, E.A. ET AL. 2010. Distance software: design and analysis of distance sampling surveys for estimating population size. Journal of Applied Ecology 47: 5-14.

THOMAS, L., WILLIAMS, R. & SANDILANDS, D. 2007. Designing line transect surveys for complex survey regions. Journal of Cetacean Research and Management 9: 1-13.

THOMAS, R. & MEDEIROS, R. 2010. Storm-petrels in Portugal: results from 2007-2008 surveys. A Rocha Portugal Observatory Report for 2007-08. Portimão, Portugal: Associação A Rocha.

TRENKEL, V.M., BUCKLAND, S.T., MCLEAN, C. & ELSON, D.A. 1997. Evaluation of aerial line transect methodology for estimating red deer (Cervus elaphus) abundance in Scotland. Journal of Environmental Management 50: 39-50.

VINGADA, J.V. & EIRA, C. 2018. Conservação de Cetáceos e Aves Marinhas em Portugal Continental. O projeto LIFE+ MarPro. Relatório final do projecto NAT/PT/00038. Aveiro, Portugal: Departamento de Biologia da Universidade de Aveiro.

WINIARSKI, K.J., MILLER, D.L., PATON, P.W.C. & MCWILLIAMS, S.R. 2013. A spatially explicit model of wintering common loons: Conservation implications. Marine Ecology Progress Series 492: 273-283.

Search by author or title:

Browse previous volumes: