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 appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely 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.
The global population is estimated to number c.1,400,000-2,100,000 individuals (Wetlands International 2015). The European population is estimated at 401,000-512,000 pairs, which equates to 803,000-1,020,000 mature individuals (BirdLife International 2015).
The overall population trend is increasing, although some populations may be stable and others have unknown trends (Wetlands International 2015). This species has undergone a small or statistically insignificant increase over the last 40 years in North America (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). Within its European range it is estimated to be increasing (BirdLife International 2015).
This species has an extremely large distribution, being found on every continent except South America and Antarctica. Colonies in North America are restricted to the north-east, although individuals do winter further south up to the tip of Florida (U.S.A.). Breeding colonies are also found in western Greenland (to Denmark). In Europe, the it can be found along most of the Atlantic coast, as well as throught the Mediterranean and in large areas of Eastern Europe. In Africa, it can be found wintering of the northern coast as well as along the Nile, and breeding year-round on the north-west coast, in pockets of central-east Africa and in South Africa. Summer breeding occurs in patches through much of central Asia up to eastern China, year-round wintering occurs in India and southern China, and birds can be found wintering in south-east Asia. Finally, it can be found in most of Australia except central regions, and it also winters in New Zealand.
Behaviour Throughout its range the species is sedentary or locally dispersive, with northerly populations also making strong migratory movements (del Hoyo et al. 1992). The timing of breeding varies geographically, occurring all year round (del Hoyo et al. 1992) or coinciding with the rains in the tropics (Johnsgard 1993) and peaking between April and June in the temperate regions of the Northern Hemisphere (del Hoyo et al. 1992). The species breeds in mixed-species colonies (del Hoyo et al. 1992) of 10-500 pairs (Nelson 2005) (occasionally up to 1,000 pairs) (Brown et al. 1982), the size of the colony depending upon the extent of nearby feeding areas (Nelson 2005). It is usually a solitary feeder (Brown et al. 1982) but may form large fishing flocks in some areas (del Hoyo et al. 1992). It also roosts communally at nesting sites or in major feeding areas and flies in flocks of varying sizes (Brown et al. 1982). Off the coasts of eastern Jutland and of Læsø, Denmark, flocks sizes of up to 890 individuals were observed (Petersen et al 2003). Feeding is exclusively diurnal. Habitat The species frequents both coastal and inland habitats (Brown et al. 1982, del Hoyo et al. 1992, Johnsgard 1993, Snow and Perrins 1998, Nelson 2005). In marine environments it occurs in sheltered coastal areas on estuaries (del Hoyo et al. 1992), saltpans, coastal lagoons (del Hoyo et al. 1992, Johnsgard 1993), mangrove swamps, deltas (Johnsgard 1993) and coastal bays (Brown et al. 1982), requiring rocky shores, cliffs and islets for nesting (del Hoyo et al. 1992) but generally avoiding deep water and rarely extending far offshore (Snow and Perrins 1998). It also inhabits fresh, brackish or saline inland wetlands (Nelson 2005) including lakes, reservoirs, wide rivers, flood waters (del Hoyo et al. 1992), deep marshes with open water, swamps and oxbow lakes (Johnsgard 1993), requiring trees, bushes, reedbeds or bare ground for nesting (del Hoyo et al. 1992) and avoiding overgrown, small, very shallow or very deep waters (Nelson 2005). Diet The species' diet consists predominantly of fish, including sculpins, Capelin, gadids (Gremillet et al 2004) and flatfish (Leopold et al 1998) as well as crustaceans, amphibians (del Hoyo et al. 1992), molluscs and nestling birds (Brown et al. 1982). At sea the species preys mostly on bottom-dwelling fish, occasionally also taking shoaling fish in deeper waters (del Hoyo et al. 1992). It is a generalist, having been shown to feed on at least 22 different fish species (Gremillet 1997). Breeding site The nest varies from a depression (Nelson 2005) to a platform of sticks, reeds and seaweed (del Hoyo et al. 1992). On the coast the species nests on inshore islands, cliffs, stacks, amongst boulders and occasionally on artificial structures (del Hoyo et al. 1992), also nesting inland on trees or bushes, in reedbeds or on bare ground (del Hoyo et al. 1992). The species usually nests in mixed-species colonies, often re-using sites and nests from year to year (del Hoyo et al. 1992). Foraging range The Great Cormorant has a largely neritic distribution. At sea, it rarely wanders far from the coast, preferring sheltered areas and estuaries where it normally feeds in shallow water. It preys mainly on benthic fish species. It is rarely observed to dive below 10 m (BirdLife International 2000, Petersen et al 2003, Gremillet et al 2004) although it has been recorded at up to 35 m (Gremillet et al 2004). Several studies have shown that this species is able to forage up to 20-25 km from its wintering roosts or breeding colonies. Most foraging trips are confined to within 10 km of the colony (Gremillet 1997, BirdLife International 2000, Petersen et al 2003), but trips up to a 35 km radius have been recorded (Gremillet 1997). Off the coasts of eastern Jutland and at Læsø, Denmark, 75% of recorded birds were seen within 3 km of the coast (Petersen et al 2003). Preferred habitats include granitic boulder, since this is the favoured habitat of labrids, the commonest prey in the diet (Gremillet 1997). The species is also likely to select sandy areas with a high abundance of flatfish or rocky substrates where gobies, wrasse, sea scorpions and small gadoids occur (BirdLife International 2000).
The species is often persecuted by the aquaculture industry and may be shot, drowned or poisoned in attempts to control numbers (Carss 1994) or for hunting (Bzoma et al. 2011). It may also suffer from disturbance from coastal wind farms (wind turbines) (Bradbury et al. 2014), and is susceptible to avian influenza (Melville and Shortridge 2006) and Newcastle disease (Kuiken 1999) so may be threatened by future outbreaks of these viruses (Kuiken 1999, Melville and Shortridge 2006). Recreational activities taking place at sea may also cause displacement from critical habitat. The species is susceptible to oil spills across its range. It is also highly vulnerable to bycatch in gillnets (Žydelis et al. 2013), and the species is also caught in longlines (Bellebaum et al. 2009) and purse seines (Oliveira et al. 2015). Utilisation The species is hunted for recreation and is sold at commercial food markets in Iran (Balmaki and Barati 2006).
Conservation Actions Underway
The species is listed under the African Eurasian Waterbird Agreement. Within its European range the species occurs in 242 Important Bird Areas. Within the EU it is listed in 245 Special Protection Areas. It may be possible to alleviate conflicts between this species and fisheries by using such strategies as preventing birds from landing on fish ponds through disturbance, or creating unsuitable feeding conditions (Kirby et al. 1996).
Conservation Actions Proposed
The following information refers to the species's European range only: Continued monitoring of population control measures.
Text account compilers
Hatchett, J., Ekstrom, J., Ashpole, J, Malpas, L., Butchart, S., Calvert, R.
BirdLife International (2018) Species factsheet: Phalacrocorax carbo. Downloaded from http://www.birdlife.org on 21/07/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 21/07/2018.