Cory’s Shearwater (Calonectris diomedea) is being split: request for information on C. diomedea and C. borealis

The provisional deadline for comments on this discussion is February 2015.

This is part of a consultation on the Red List implications of extensive changes to BirdLife’s taxonomy for non-passerines.

Lynx Edicions and BirdLife International will soon publish the HBW-BirdLife Illustrated Checklist of the Birds of the World, building off the Handbook of the Birds of the World series, and BirdLife’s annually updated taxonomic checklist.

The new Checklist will be based on the application of criteria for recognising species limits described by Tobias et al. (2010). Full details of the specific scores and the basis of these for each new taxonomic revision will be provided in the Checklist.

Following publication, an open and transparent mechanism will be established to allow people to comment on the taxonomic revisions or suggest new ones, and provide new information of relevance in order to inform regular updates. We are also actively seeking input via a discussion topic here regarding some potential taxonomic revisions that currently lack sufficient information.

The new Checklist will form the taxonomic basis of BirdLife’s assessments of the status of the world’s birds for the IUCN Red List. The taxonomic changes that will appear in volume 1 of the checklist (for non-passerines) will begin to be incorporated into the 2014 Red List update, with the remainder, and those for passerines (which will appear in volume 2 of the checklist), to be incorporated into subsequent Red List updates.

Preliminary Red List assessments have been carried out for the newly split or lumped taxa. We are now requesting comments and feedback on these preliminary assessments.

Cory’s Shearwater Calonectris diomedea is being split into C. diomedea and C. borealis, following the application of criteria set out by Tobias et al. (2010) and consultation of genetic evidence (Gómez-Díaz et al. 2009, Genovart et al. 2013).

These species will be provisionally listed as Least Concern in the 2014 Red List update; however, this discussion will remain open for comments until early 2015, to allow the results of the ongoing regional Red List assessment for all European birds to be taken into account.

Prior to this taxonomic change, C. diomedea (BirdLife species factsheet) was listed as being of Least Concern, on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN Red List criteria. Despite this, the species has previously been listed as Vulnerable at the regional level in Europe, which holds more than 75% of the global population, owing to the suspicion of a rapid population decline (BirdLife International 2004). The pre-split species is still regarded as having an unfavourable conservation status in Europe (Carboneras et al. 2013), although this may change when the results of the European Red List assessment are available.

C. diomedea (as defined following the taxonomic change) breeds in Algeria, Croatia, France, Greece, Italy, Malta, Spain (excluding the Canary Islands), Tunisia and Turkey (Derhé 2012). The majority of the population is thought to spend the non-breeding season in the Atlantic, including areas off the west coast of Africa and east coast of Brazil (Péron et al. 2012).

The species has been estimated to have a population of 142,478-222,886 pairs (Derhé 2012, Carboneras et al. 2013), assumed here to be equivalent to c.285,000-446,000 mature individuals. This estimate follows recent surveys of the largest colony on Zembra Island, Tunisia, which resulted in an alternative revised estimate for the total breeding population of 179,000-193,000 pairs (Defos du Rau et al. 2012).

The species’s population is estimated and projected to be declining by c.2% over three generations (1980-2038), although this is based on data from only 6% of the population (Derhé 2012, Carboneras et al. 2013). Until estimates of adult survival and breeding probabilities in Tunisia, as well as other important locations (e.g. Italy), are available, any estimate of the global population trend for the species is regarded as purely speculative (Carboneras et al. 2013). This taxon has been classified as Endangered at the national level in Spain, owing to a projected decline of 65% over three generations into the future (Carboneras 2004).

The main threats to C. diomedea include the impacts of invasive, non-native mammals and mortality from fisheries bycatch (Derhé 2012, Carboneras et al. 2013). Recent studies have highlighted the pressures imposed by introduced mammal species, and colonies have shown marked increases in breeding success during mammal control measures (e.g. Igual et al. 2006, Pascal et al. 2008). C. diomedea is one of the most frequent seabird species to occur in bycatch in the Mediterranean (Valeiras and Caminas 2003, García-Barcelona et al. 2010, Laneri et al. 2010), with estimates of the number of individuals killed annually by Spanish fleets ranging from 200 (García-Barcelona et al. 2010) to 467-1,867 (estimated 4-6% of the local breeding population; Belda and Sanchez 2001). There have been fewer assessments of the impacts of long-line and other national fisheries on this species. Results from a questionnaire suggest an annual bycatch of up to 1,220 individuals of C. diomedea by Maltese fleets (8.5-10% of the breeding population), although this is likely to be an over-estimate skewed by high bycatch in a small number of vessels (Dimech et al. unpubl. per Derhé 2012). The species may also suffer significant bycatch in its non-breeding range (e.g. Granadeiro et al. 2006).

C. borealis breeds on the Azores and Madeira (>85% of the global population), Canary Islands (c.15%) and Berlengas Islands (a few pairs) (Granadeiro et al. 2006, Derhé 2012). The majority of the population is thought to spend the non-breeding season in the Atlantic. The species’s population is estimated to comprise c.251,100-251,300 pairs (Derhé 2012), assumed to be equivalent to c.502,200-502,600 mature individuals.

This species is estimated and projected to be increasing by c.100% over three generations (1980-2038), due predominantly to a population recovery at Selvagem Grande (Savage Islands, Madeira archipelago), of an estimated 4.6% per year since 1980 (Granadeiro et al. 2006). This follows a series of mass culling events in the 1970s, carried out by Portuguese and Spanish fishermen, which reduced the colony by c.90% from c.140,000 pairs. Since 1977, strict protection has been enforced and the population started a steady recovery; however, between 1995 and 1998 a decline of more than 13% was reported, before monitoring work was interrupted. Following fieldwork in 2005, the colony was estimated to number c.30,000 pairs (Granadeiro et al. 2006), which implies an overall decline of c.110,000 pairs since the mid-20th century. Following the surveys in 2005, it was estimated that at an annual growth rate of 5% it would take another 35 years for the colony to reach its numbers prior to the culling events (Granadeiro et al. 2006).

The current estimate for an increasing overall population trend is based on data from only 13% of the population and the assumption that the Azorean population is stable, which is thought unlikely to be the case (Derhé 2012). Determining the trend in the Azores is considered crucial to estimating the global trend for C. borealis (Derhé 2012). It is suspected that the population may be declining in the Azores, although this has not been confirmed, and reported rapid declines (43% decline during 1996-2001; Bolton 2001) may be caused by inter-annual variation in colony attendance (Chastel et al. 1993, Jenouvrier et al. 2005), along with behavioural differences between census years (Bolton 2001, Fontaine et al. 2011). The taxon has declined on the Canary Islands and has been listed as Vulnerable at the national level in Spain, owing to an estimated and projected decline of at least 30% over three generations (Lorenzo 2004).

C. borealis is threatened by the impacts of introduced mammals and shows marked increases in breeding success following mammal control actions (Zino et al. 2008). Other threats on the Azores include the poaching of chicks on one island (500-1,500 chicks taken annually on Santa Maria island; J. Bairos per Fontaine et al. 2011), and mortality of fledglings caused by artificial lights (Fontaine et al. 2011). The population on Selvagem Grande is not thought to be suffering unsustainable mortality from fisheries bycatch, although it may not be representative of other Atlantic islands occupied by the species (Granadeiro et al. 2006). A study by Ramos et al. (2012) utilising long-term capture-recapture data and year-round tracking data for birds on Selvagem Grande suggests that incidental bycatch by long-line fisheries contributes to a decrease in adult survival probability during the breeding season. The species may also suffer the impacts of bycatch in its non-breeding range (e.g. Granadeiro et al. 2006).

Further information is requested on the status of C. diomedea and C. borealis, with particular emphasis on population trends in the Azores, Tunisia and Italy.


Belda, E. J. and Sanchez, A. (2001) Seabird mortality on longline fisheries in the western Mediterranean: factors affecting bycatch and proposed mitigating measures. Biological Conservation 98: 357–363.

BirdLife International (2004) Birds in Europe: population estimates, trends and conservation status. Cambridge, UK: BirdLife International (BirdLife Conservation Series 12).

Bolton, M. (2001) Census of Cory’s Shearwaters Calonectris diomedea in the Azores Archipelago 2001-Final Report. Department of Oceanography and Fisheries, University of the Azores, Horta, Portugal.

Carboneras, C. (2004) Pardela Cenicienta, Calonectris diomedea diomedea. Pp 39-43 in Madroño, A., González, C. and Atienza, J. C. (Eds.) Libro Rojo de las Aves de España. Madrid, Spain: Dirección General para la Biodiversidad-SEO/BirdLife.

Carboneras, C., Derhé, M. and Ramirez, I. (2013). Update on the population status and distribution of Mediterranean shearwaters. Report to Seventh Meeting of the ACAP Advisory Committee, La Rochelle, France, 6-10 May 2013.

Chastel, O., Weimerskirch, H. and Jouventin, P. (1993) High annual variability in reproductive success and survival of an Antarctic seabird, the snow petrel Pagodroma nivea. Oecologia 94: 278–285.

Defos du Rau, P., Bourgeois, K., Ruffino, L., Dromzée, S., Ouni,R., Abiadh, A., Estève, R., Durand, J-P., Anselme, L., Faggio, G., Yahya, J.M., Peters, P., Rguibi, H., Renda, M., Miladi, B., Hamrouni, H., Alilech, S., Ben Dhafer, A., Nefla,A., Jaouadi, W., Agrebi, S. and Renou, S. (2012) New assessment of the world largest colony of Scopoli’s Shearwater Calonectris diomedea. Pp 26–28 in Yésou, P., Baccetti, N. and 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. Alghero, Italy: Medmaravis.

Derhé, M. (2012) Developing a Population Assessment for Scopoli’s and Cory’s Shearwaters Calonectris diomedea/Calonectris borealis. Pp 29–38 in Yésou, P., Baccetti, N. and 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. Alghero, Italy: Medmaravis.

Fontaine, R., Gimenez, O. and Bried, J. (2011) The impact of introduced predators, light-induced mortality of fledglings and poaching on the dynamics of the Cory’s shearwater (Calonectris diomedea) population from the Azores, northeastern subtropical Atlantic. Biological Conservation 144: 1998–2011.

García-Barcelona, S., Ortiz de Urbina, J. M., de la Serna, J. M., Alot, E. and Macias, D. (2010) Seabird bycatch in Spanish Mediterranean large pelagic longline fisheries, 2000-2008. Aquatic Living Resources 23: 363–371.

Genovart, M., Thibault, J.-C., Igual, J. M., Bauzá-Ribot, M. del M., Rabouam, C. and Bretagnolle, V. (2013) Population structure and dispersal patterns within an between Atlantic and Mediterranean populations of a large-range pelagic seabird. PLoS ONE 8(8): e70711. doi:10.1371/journal.pone.0070711.

Gómez-Díaz, E., González-Solís, J. and Peinado, M. A. (2009) Population structure in a highly pelagic seabird, the Cory’s Shearwater Calonectris diomedea: an examination of genetics, morphology and ecology. Marine Ecology Progress Series 382: 197–209.

Granadeiro, J. P., Dias, M. P., Rebelo, R., Santos, C. D. and Catry, P. (2006) Numbers and Population Trends of Cory’s Shearwater Calonectris diomedea at Selvagem Grande, Northeast Atlantic. Waterbirds 29(1): 56–60.

Igual, J. M., Foreroz, M. G., Gomez, T., Oruetas, J. F. and Oro, D. (2006) Rat control and breeding performance in Cory’s shearwater (Calonectris diomedea): effects of poisoning effort and habitat features. Animal Conservation 9: 59–65.

Jenouvrier, S., Barbraud, C., Cazelles, B. and Weimerskirch, H. (2005) Modelling population dynamics of seabirds: importance of the effects of climate fluctuations on breeding proportions. Oikos 108: 511–522.

Laneri, K., Louzao, M., Martinez-Abrain, A., Arcos, J. M., Belda, E. J., Guallart, J., Sanchez, A., Gimenez, M., Maestre, R. and Oro, D. (2010) Trawling regime influences longline seabird bycatch in the Mediterranean: new insights from a small-scale fishery. Marine Ecology Progress Series 420: 241–252.

Lorenzo, J. A. (2004) Pardela Cenicienta, Calonectris diomedea borealis. Pp 43-45 in Madroño, A., González, C. and Atienza, J. C. (Eds.) Libro Rojo de las Aves de España. Madrid, Spain: Dirección General para la Biodiversidad-SEO/BirdLife.

Pascal, M., Lorvelec, O., Bretagnolle, V. and Culioli, J. M. (2008) Improving the breeding success of a colonial seabird: a cost-benefit comparison of the eradication and control of its rat predator. Endangered Species Research 4: 267­–276.

Péron, C., Grémillet, D., Culioli, J.-M., Faggio, G., Gillet, P., Mante, A. and Vidal, P. (2012) Exploring marine habitats of two shearwater species breeding on French Mediterranean islands. Pp 19–25 in Yésou, P., Baccetti, N. and 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. Alghero, Italy: Medmaravis.

Ramos, R., Granadeiro, J. P., Nevoux, M., Mougin, J.-L., Dias, M. P. and Catry, P. (2012) Combined Spatio-Temporal Impacts of Climate and Longline Fisheries on the Survival of a Trans-Equatorial Marine Migrant. PLoS ONE 7(7): e40822. doi:10.1371/journal.pone.0040822

Tobias, J. A., Seddon, N., Spottiswoode, C. N., Pilgrim, J. D., Fishpool, L. D. C. and Collar, N. J. (2010) Quantitative criteria for species delimitation. Ibis 152: 724–746.

Valeiras, J. and Caminas, J. A. (2003) The incidental capture of seabirds by Spanish drifting longline fisheries in the western Mediterranean Sea. Scientia Marina 67: 65–68.

Zino, F., Hounsome, M. V., Buckle, A. P. and Biscoito, M. (2008) Was the removal of rabbits and house mice from Selvagem Grande beneficial to the breeding of Cory’s shearwaters Calonectris diomedea borealis? Oryx 42: 151–154.

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  3. Archived 2012-2013 topics: Amsterdam Albatross (Diomedea amsterdamensis): downlist to Endangered?
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2 Responses to Cory’s Shearwater (Calonectris diomedea) is being split: request for information on C. diomedea and C. borealis

  1. Joe Taylor says:

    The following comments were received from Steffen Oppel and the Portuguese Society for the Study of Birds (SPEA) on 4 March 2014:

    We estimated the breeding population on Corvo (the smallest of the Azorean islands, but historically believed to have the largest Cory’s colony) at 6326 (3735-10,524)breeding pairs in 2012: Oppel S, Hervias S, Oliveira N, Pipa T, Silva C, Geraldes P, Goh M, Immler E, McKown M (2014) Estimating population size of a nocturnal burrow-nesting seabird using acoustic monitoring and habitat mapping. Nature Conservation 6:1-13 10.3897/natureconservation.6.6890

    There is ongoing predation by rats and cats, and cats appear to be far worse than rats on Corvo. Due to the interaction of cats and rats we advise against eradicating rats unless you can simultaneously eradicate cats – which is very difficult on an island where people live (and have cats): Hervías S, Henriques A, Oliveira N, Pipa T, Cowen H, Ramos JA, Nogales M, Geraldes P, Silva C, Ruiz de Ybáñez R, Oppel S (2013) Studying the effects of multiple invasive mammals on Cory’s shearwater nest survival. Biol Invasions 15:143-155

  2. Pierre Yésou says:

    C. borealis: I cannot see why you wrote ” The majority of the population is thought to spend the non-breeding season in the Atlantic “, since there are plenty of data showing that the vast majority of the population does spend the non-breeding season in the Atlantic, with some extension to the Indian Ocean off South Africa, and very marginal occurence in the English Cannel and North Sea (which tend to be considered as part of the Atlantic realm) and Caribbean Sea.

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