Cory's Shearwater Calonectris borealis


Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (extent of occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is difficult to determine however the population is not believed to be declining sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

Population justification
The European population is estimated at 252,000-253,000 pairs, which equates to 504,000-507,000 mature individuals (BirdLife International 2015).

Trend justification

The trend of the European breeding population is difficult to quantify owing to gaps in the data. However the largest population (Azores, with c. 75% of the European population) is not thought to be declining appreciably. It is therefore unlikely that the species is declining at a rate approaching >30% over ten years or three generations. A population recovery has been reported for the population on Selvagem Grande (Savage Islands, Madeira archipelago), with an estimated increase of 4.6% per year since 1980 (Granadeiro et al. 2006).

Distribution and population

This species breeds on the Azores and Madeira (>85% of the global population, plus a few pairs on the Berlengas Islands off the Portuguese mainland), Portugal, and on the Canary Islands, Spain (c. 15% of the global population; Granadeiro et al. 2006, Derhé 2012). The vast majority of the population spends the non-breeding season in the Atlantic.

A population recovery is reported for Selvagem Grande (Savage Islands, Madeira archipelago), the largest Cory's Shearwater colony in the world, with an estimated increase of 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 largest colony in the Azores is on the island of Corvo, where the latest population estimate was >6,000 pairs (3,735-10,524) in 2012 however the colony may have been much larger in the past (Oppel et al. 2014).

The population size trend is difficult to determine owing to gaps in the data, and is therefore considered unknown according to the European Red List of Birds (BirdLife International 2015). The population in the Azores was reported to be stable between 2001 and 2012 (BirdLife International 2015). However rapid declines have been reported in the Azores (43% decline during 1996-2001; Bolton 2001) which may be caused by inter-annual variation in colony attendance (Jenouvrier et al. 2005), along with behavioural differences between census years (Bolton 2001, Fontaine et al. 2011). The taxon 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).


Pelagic movements are easily divided into frequent foraging trips around the breeding areas, rapid, long-distance migrations, and smaller-scale movements within a well defined wintering ground (González-Solís et al. 2007). Breeding starts in April on barren offshore islands, occupying cliffs, caves and boulder fields (del Hoyo et al. 1992). Breeding individuals in the Canary Islands show a unimodel foraging strategy, concentrating on highly productive regions of the African continental shelf (Navarro and González-Solís 2009). Diet is mostly squid, which are obtained mainly by surface-seizing. It is regularly attracted to trawlers to feed on offal (del Hoyo et al. 1992).


The species is threatened by the impacts of introduced mammals (including rats, cats and mice [Hervías et al. 2013]) 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). It is the main seabird species caught as bycatch by the Spanish long-line fleet in the western Mediterranean (Báez et al. 2014).

Conservation actions

Conservation Actions Underway
The following information refers to the species's European range only: In Europe most important breeding areas are in protected areas (Madroño et al. 2004, Cabral et al. 2005). In Spain, sporadic counts of breeding populations occur in some colonies, mostly in the Balearic Islands but in the Columbretes, counts are more regular. Reproductive success is also monitored in the Chafarinas (Madroño et al. 2004). A study of the incidental mortality of seabirds in waters around the Columbretes Islands (SEO/BirdLife, General Secretariat of Fisheries) found high numbers of this species were killed by longline fisheries, however mortality could be reduced by avoiding setting lines around sunrise and sunset (Belda and Sanchez 2001). Research projects and awareness campaigns, some of which were financed through the LIFE Programme have taken place in Portugal (Cabral et al. 2005).

Conservation Actions Proposed
The following information refers to the species's European range only: Adequate protection (e.g. through SPAs) of all breeding areas both current and historical should be ensured. Actively managing the breeding colonies (eliminating predators, recreating the breeding habitat) and removing predators from the former breeding colonies to promote the natural return of the species, will also help secure the species. The proper use of corrective measures in longline fisheries to avoid accidental capture of birds should be promoted and specific corrective measures to prevent accidental capture of the species in longline fisheries should be developed, in collaboration with the fishing industry. Marine areas which are important for the conservation of the species should be designated SPAs and assessments of the environmental impact of new developments and activities that are planned need to be established. Conduct national censuses of this species and monitor breeding colonies to determine accurate populaton trends. Water sports in the vicinity of breeding colonies should be regulated, especially at night, in order to avoid disturbing the birds. The regulation of artificial lighting in the breeding areas and adjacent coastal areas, to minimize their impact particularly on young birds at the time of fledging, is also important (Madroño et al. 2004).


Text account compilers
Butchart, S., Calvert, R., Ekstrom, J., Newton, P., Symes, A., Taylor, J. & Ashpole, J

Oppel, S., Portuguese Society for the Study of Birds (SPEA) & Yésou, P.

Recommended citation
BirdLife International (2017) Species factsheet: Calonectris borealis. Downloaded from on 19/10/2017. Recommended citation for factsheets for more than one species: BirdLife International (2017) IUCN Red List for birds. Downloaded from on 19/10/2017.