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New population estimates of a critically endangered species, the Balearic Shearwater Puffinus mauretanicus, based on coastal migration counts


The Balearic Shearwater Puffinus mauretanicus is considered one of the most threatened seabirds in the world, with the breeding population thought to be in the range of 2,000–3,200 breeding pairs, from which global population has been inferred as 10,000 to 15,000 birds. To test whether the actual population of Balearic Shearwaters is larger than presently thought, we analysed the data from four land-based census campaigns of Balearic Shearwater post-breeding migration through the Strait of Gibraltar (mid-May to mid-July 2007–2010). The raw results of the counts, covering from 37% to 67% of the daylight time throughout the migratory period, all revealed figures in excess of 12,000 birds, and went up to almost 18,000 in two years. Generalised Additive Models were used to estimate the numbers of birds passing during the time periods in which counts were not undertaken (count gaps), and their associated error. The addition of both counted and estimated birds reveals figures of between 23,780 and 26,535 Balearic Shearwaters migrating along the north coast of the Strait of Gibraltar in each of the four years of our study. The effects of several sources of bias suggest a slight potential underestimation in our results. These figures reveal the urgent need to reformulate the population viability analysis for the species, and then if necessary reconsider its conservation status.

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Akaike, H. (1973) Information theory and an extension of the maximum likelihood principle. Pp. 267281 in Petrov, B. N. and Csake, F., eds. Proceedings of the second international symposium on information theory. Budapest, Hungary: Akademiai Kiado.
Arcos, J. M., Louzao, M. and Oro, D. (2008) Fisheries ecosystem impacts and management in the Mediterranean: Seabirds point of view. Amer. Fisheries Soc. Symp. 49: 14711479.
Arcos, J. M. (2011a) International species action plan for the Balearic Shearwater, Puffinus mauretanicus. SEO/BirdLife and BirdLife International. Available from (accessed March 2014).
Arcos, J. M. (2011b) ¿Cuántas pardelas baleares hay? Discrepancias entre los censos en colonias y en el mar. Pp. 117122 in Valeiras, X., Muñoz, G., Bermejo, A., M.Arcos, J. and Paterson, A. M., eds. Actas del 6° Congreso del GIAM y el Taller internacional sobre la Ecología de Paiños y Pardelas en el sur de Europa. Boletín del Grupo Ibérico de Aves Marinas 34.
Arroyo, G. M., Cuenca, D., Barrios, L., de la Cruz, A., Ramírez, J., Onrubia, A., González, M. and Román, A. (2011) Seguimiento de la migración de aves marinas en el Estrecho de Gibraltar (SO España): el Programa Migres Marinas. Pp. 4347 in Valeiras, X., Muñoz, G., Bermejo, A., Arcos, J. M., and Paterson, A. M., eds. Actas del 6° Congreso del GIAM y el Taller internacional sobre la Ecología de Paiños y Pardelas en el sur de Europa. Boletín del Grupo Ibérico de Aves Marinas, 34.
Baillie, J. E. M., Hilton-Taylor, C. and Stuart, S. N., eds. (2004) IUCN Red List of Threatened Species. A global species assessment. Gland, Switzerland and Cambridge, UK: IUCN.
Barbraud, C., Delord, K., Marteau, C. and Weimerskirch, H. (2009) Estimates of population size of white-chinned petrels and grey petrels at Kerguelen Islands and sensitivity to fisheries. Anim. Conserv. 12: 258265
Bibby, C. J., Burgess, N. D., Hill, D. A. and Mustoe, S. H., eds. (2000) Bird census techniques. 2nd edition. London, UK: Academic Press.
BirdLife International (2004) Birds in Europe: population estimates, trends and conservation status. Cambridge, UK: BirdLife International. (BirdLife International Series N°12).
BirdLife International (2014) Species factsheet: Puffinus mauretanicus. Downloaded from on 19/04/2014.
Del Hoyo, J., Elliott, A. and Sargatal, J., eds. (1992) Handbook of the birds of the world. Vol I: Ostrich to ducks. Barcelona, Spain: Lynx Edicions.
Dias, M. P., Granadeiro, J. P. and Catry, P. (2012) Do seabirds differ from other migrants in their travel arrangements? On route strategies of Cory’s Shearwater during its trans-equatorial journey. PLoS ONE 7(11): e49376. doi:10.1371/journal.pone.0049376
Gilbert, G., Gibbons, D. W. and Evans, J. (1998) Bird monitoring methods. RSPB, UK: Sandy.
Guilford, T., Wynn, R., McMinn, M., Rodríguez, A., Fayet, A., Maurice, L., Jones, A. and Meier, R. (2012) Geolocators reveal migration and pre-breeding behaviour of the Critically Endangered Balearic Shearwater Puffinus mauretanicus . PLoS ONE 7(3): e33753. doi. 10.1371/journal.pone.0033753
Hashmi, D. (2000) Opportunities for monitoring seabirds and cetaceans in the Strait of Gibraltar. Pp. 176191 in: Yesou, P. and Sultana, J., eds. Monitoring and conservation of birds, mammals and sea turtles in the Mediterranean and Black Seas: Proceedings of the 5th Medmaravis Symposium. Gozo, Malta.
Hastie, T. and Tibshirani, R. J. (1990) Generalized additive models. London, UK: Chapman and Hall.
Heaney, V., Ratcliffe, N., Brown, A., Robinson, P. J. and Lock, L. (2002) The status and distribution of European Storm-petrels Hydrobates pelagicus and Manx Shearwaters Puffinus puffinus on the isles of Scilly. Atlantic Seabirds 4: 116.
IUCN (2001) IUCN Red List categories and criteria : Version 3.1. Gland, Switzerland and Cambridge, UK: IUCN Species Survival Commission. Available from (accessed January 2012).
Laneri, K., Louzao, M., Martínez-Abraín, A., Arcos, J. M., Belda, E. J., Guallart, J., Sánchez, A., Giménez, M., Maestre, R. and Oro, D. (2010) Trawling regime influences longline seabird bycatch in the Mediterranean: new insights from a small-scale fishery. Mar. Ecol. Progr. Ser. 420: 241252.
Lewison, R., Oro, D., Godley, B., Underhill, L., Bearhop, S., Wilson, R., Ainley, D., Arcos, J., Boersma, P., Borboroglu, P., Boulinier, T., Frederiksen, M., Genovart, M., González-Solís, J., Green, J. A., Grémillet, D., Hamer, K. C., Hilton, M., , G., Hyrenbach, K. D., Martínez-Abraín, A., Montevecchi, W. A., Phillips, R. A., Ryan, P. G., Sagar, P., Sydeman, W. J., Wanless, S., Watanuki, Y., Weimerskirch, H. and Yorio, P. (2012) Research priorities for seabirds: improving conservation and management in the 21st century. Endangered Species Res. 17: 93121.
Louzao, M., Arcos, J. M., Laneri, K., Martínez-Abraín, A., Belda, E., Guallart, J., Sánchez, A., Giménez, M., Maestre, R. and Oro, D. (2011) Evidencias de la captura incidental de pardela balear en el mar. Pp. 165168 in Valeiras, X., Muñoz, G., Bermejo, A., Arcos, J. M. and Paterson, A. M., eds. Actas del 6° Congreso del GIAM y el Taller internacional sobre la Ecología de Paiños y Pardelas en el sur de Europa. Boletín del Grupo Ibérico de Aves Marinas, 34.
Louzao, M., Igual, J. M., McMinn, M., Aguilar, J. S., Triay, R. and Oro, D. (2006) Small pelagic fish, trawling discards and breeding performance of the critically endangered Balearic Shearwater: improving conservation diagnosis. Mar. Ecol. Progr. Ser. 318: 247254.
Mace, G. M., Collar, N. J., Gaston, K. J., Hilton-Taylor, C. and Akçakaya, H. R. (2008) Quantification of extinction risk: the background to IUCN's system for classifying threatened species. Conserv. Biol. 22: 14241442.
Mateos-Rodríguez, M. and Arroyo, G. M. (2011) Ocean surface winds drive local-scale movements within long-distance migrations of seabirds. Mar. Biol. 158: 329339.
Mateos-Rodríguez, M., Arroyo, G. M., Rodríguez, A., Cuenca, D. and De La Cruz, A. (2010) Calibration of visually estimated distances to migrating seabirds with radar measurements. J. Field Ornithol. 81: 302309.
Mateos-Rodríguez, M., Thomas, L. and Arroyo, G. M. (2012) The development and use of a method to fill time gaps in migration counts. Condor 114: 513522.
Mouriño, J., Arcos, F., Salvadores, R., Sandoval, A. and Vidal, C. (2003) Status of the Balearic Shearwater (Puffinus mauretanicus) on the Galician coast (NW Iberian Peninsula). Scientia Marina 62 suppl. 2: 135142.
Navarro, J., Louzao, M., Igual, J. M., Oro, D., Delgado, A., Arcos, J. M., Genovart, M., Hobson, K. A. and Forero, M. G. (2009) Seasonal changes in the diet of a critically endangered seabird and the importance of trawling discards. Mar. Biol. 156: 25712578.
Newton, I. (2008) The migration ecology of birds. London: Academic Press.
Oro, D., Aguilar, J. S., Igual, J. M. and Louzao, M. (2004) Modelling demography and extinction risk in the endangered Balearic Shearwater. Biol. Conserv. 116: 93102.
Paterson, A. M. (1997) Las aves marinas de España y Portugal. Barcelona, Spain: Lynx Edicions.
Programa, Migres. (2009) Seguimiento de la migración de las aves en el Estrecho de Gibraltar: resultados del Programa Migres 2008. Migres Revista de Ecología 1: 83101.
R Development Core Team. (2010) R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing. <>
Rayner, M. J., Clout, M. N., Stamp, R. K., Imber, M. J., Brunton, D. H. and Hauber, M. E. (2007) Predictive habitat modelling for the population census of a burrowing seabird: a study of the endangered Cook’s petrel. Biol. Conserv. 138: 235247.
Rodríguez, A. and McMinn, M. (2002) Las cuevas: último refugio de la Pardela Balear Puffinus mauretanicus (Aves, Procellariidae). Boletín Sedeck 3: 128133.
Rodríguez, A. and McMinn, M. (2005) Population and distribution of the breeding colonies of Balearic Shearwater Puffinus mauretanicus Lowe 1921. Poster presentation, 2nd International Manx Shearwater workshop, Belfast, UK.
Ruiz, A. and Martí, R. (2004) La Pardela Balear. Madrid: SEO/BirdLife-Conselleria de Medi Ambient del Govern de les Illes Balears.
Stratoudakis, Y. (1999) Recommendations for improving the estimation of the number of seabirds potentially sustained by fisheries discards. Mar. Ecol. Progr. Ser. 176: 307309.
Tellería, J. L. (1981) La migración de las aves por el Estrecho de Gibraltar. Vol. 2. Aves no planeadoras. Madrid, Spain: Universidad Complutense.
Wood, S. N. (2006) Generalized Additive Models. An introduction with R. Boca Raton, Florida: Chapman and Hall/CRC.
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Bird Conservation International
  • ISSN: 0959-2709
  • EISSN: 1474-0001
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