Skip to main content
    • Aa
    • Aa

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.

Corresponding author
* Author for correspondence; email:
Linked references
Hide All

This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

C. Barbraud , K. Delord , C. Marteau and H Weimerskirch . (2009) Estimates of population size of white-chinned petrels and grey petrels at Kerguelen Islands and sensitivity to fisheries. Anim. Conserv. 12: 258265

M. P.Dias , J. P.Granadeiro and PCatry . (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

T.Guilford , R.Wynn , M.McMinn , A.Rodríguez , A.Fayet , L.Maurice , A.Jones and RMeier . (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

K.Laneri , M.Louzao , A.Martínez-Abraín , J. M.Arcos , E. J.Belda , J.Guallart , A.Sánchez , M.Giménez , R.Maestre and DOro . (2010) Trawling regime influences longline seabird bycatch in the Mediterranean: new insights from a small-scale fishery. Mar. Ecol. Progr. Ser. 420: 241252.

R.Lewison , D.Oro , B.Godley , L.Underhill , S.Bearhop , R.Wilson , D.Ainley , J.Arcos , P.Boersma , P.Borboroglu , T.Boulinier , M.Frederiksen , M.Genovart , J.González-Solís , J. A.Green , D.Grémillet , K. C.Hamer , M.Hilton , G. , K. D.Hyrenbach , A.Martínez-Abraín , W. A.Montevecchi , R. A.Phillips , P. G.Ryan , P.Sagar , W. J.Sydeman , S.Wanless , Y.Watanuki , H.Weimerskirch and PYorio . (2012) Research priorities for seabirds: improving conservation and management in the 21st century. Endangered Species Res. 17: 93121.

M.Louzao , J. M.Igual , M.McMinn , J. S.Aguilar , R.Triay and DOro . (2006) Small pelagic fish, trawling discards and breeding performance of the critically endangered Balearic Shearwater: improving conservation diagnosis. Mar. Ecol. Progr. Ser. 318: 247254.

G. M.Mace , N. J.Collar , K. J.Gaston , C.Hilton-Taylor and H. RAkçakaya . (2008) Quantification of extinction risk: the background to IUCN's system for classifying threatened species. Conserv. Biol. 22: 14241442.

M. Mateos-Rodríguez and G. M Arroyo . (2011) Ocean surface winds drive local-scale movements within long-distance migrations of seabirds. Mar. Biol. 158: 329339.

M.Mateos-Rodríguez , G. M.Arroyo , A.Rodríguez , D.Cuenca and ADe La Cruz . (2010) Calibration of visually estimated distances to migrating seabirds with radar measurements. J. Field Ornithol. 81: 302309.

J.Navarro , M.Louzao , J. M.Igual , D.Oro , A.Delgado , J. M.Arcos , M.Genovart , K. A.Hobson and M. GForero . (2009) Seasonal changes in the diet of a critically endangered seabird and the importance of trawling discards. Mar. Biol. 156: 25712578.

D. Oro , J. S. Aguilar , J. M. Igual and M Louzao . (2004) Modelling demography and extinction risk in the endangered Balearic Shearwater. Biol. Conserv. 116: 93102.

M. J. Rayner , M. N. Clout , R. K. Stamp , M. J. Imber , D. H. Brunton and M. E Hauber . (2007) Predictive habitat modelling for the population census of a burrowing seabird: a study of the endangered Cook’s petrel. Biol. Conserv. 138: 235247.

YStratoudakis . (1999) Recommendations for improving the estimation of the number of seabirds potentially sustained by fisheries discards. Mar. Ecol. Progr. Ser. 176: 307309.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Bird Conservation International
  • ISSN: 0959-2709
  • EISSN: 1474-0001
  • URL: /core/journals/bird-conservation-international
Please enter your name
Please enter a valid email address
Who would you like to send this to? *


Altmetric attention score