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Range DescriptionThis speciesis endemic to the Mediterranean basin, but its precise distribution is not well known and numbers are disputed (Bourgeois and Vidal 2008). The main breeding colonies are concentrated in the central and eastern basin of the Mediterranean, from Corsica and Sardinia through the central Mediterranean, the Adriatic and the Aegean (Borg et al. 2010). The species is known to breed in France (662-1,109 pairs, 528-1,053 pairs according to BirdLife International 2015), Italy (9,000-20,000 pairs, 12,791-19,774 according to BirdLife International 2015), Malta (1,190 - 1,680 pairs, 1,660-1,980 according to BirdLife International 2015), Algeria (8-10 pairs), Tunisia (176-200 pairs), Croatia (300-500 pairs, 300-400 pairs according to BirdLife International 2015), Albania (1-10 pairs), Greece (4,000-7,000 pairs) and Bulgaria (0-10 pairs) giving a global estimate of 15,300-30,500 pairs according to Derh (2012) and 19,400-31,200 pairs according to BirdLife International (2015). Breeding is assumed in Turkey on offshore islands or mainland cliffs in the Aegean and Mediterranean, but so far no colonies have been identified and more surveys are needed (D. Sahin in litt. 2015).
A small population may also breed on the eastern Balearic Islands in Spain, although the existence of the species here is somewhat controversial, given the taxonomic uncertainty of the birds breeding in Menorca (Arcos 2011, Cur et al. 2010).During the non-breeding season birds are thought to migrate north-eastwards towards the Black Sea, although some birds may remain close to breeding colonies or disperse around the Mediterranean (Raine et al. 2013, Carboneras et al. 2014). More than 90,000 individuals were recorded passing through the Bosphorous during the non-breeding season in 2014 (D. Sahin in litt. 2015).
Population trends in Algeria, Bulgaria and Tunisia are currently unknown. Trends in Albania, Croatia, France and Turkey were reported as unknown in the short-term for the 2015 European Red List of Birds and Albania, Croatia, Greece and Turkey reported unknown trends for the long-term (BirdLife International 2015). The population has been estimated to be declining rapidly in Italy (N. Baccetti in litt. 2011), however trends reported for the European Red List of Birds suggest the population may be increasing (BirdLife International 2015). The reported increase in the Italian population is highly dependent on the trend of the most important breeding site, Tavolara, where numbers are thought to be steadily increasing (E. Dupre, L. Serra in litt. 2015). However it is not clear whether reported increases are as a result of changes in methodologies for monitoring population trends (N. Baccetti in litt. 2015). Declines have previously been reported for France (Oppel et al. 2011) and Malta (Borg and Sultana 2002, Raine et al. 2009, Sultana et al. 2011), although the Maltese population was reported as increasing in the 2015 European Red List of Birds (BirdLife International 2015) but this may be as a result of better knowledge of the species rather than a genuine increase (B. Metzger in litt. 2015). Nine colonies have gone extinct over the last 60 years (Bourgeois and Vidal 2008) and since 2009, one breeding colony off Sardinia (San Pietro Island) has been reported as absent, possibly extinct (N. Baccetti in litt. 2011). Most worryingly, breeding success at many colonies appears to be extremely low and adult survival probabilities across the western Mediterranean have been reported as too low to maintain stable populations (Oppel et al. 2011).