Data Zone
Justification of Red List category
This species is listed as Vulnerable because it has a small range, which is suspected to be undergoing a continuous and rapid decline, largely because of infrastructure and residential development, disturbance at its nesting colonies, exploitation, and marine oil pollution.
Population justification
The breeding population is estimated at 110,000 pairs (Jennings 2010) (330,000 [Jennings 2000] to fewer than 500,000 [H. King in litt. 2005] individuals).
Trend justification
In the northern population, c.12 colonies have become extinct (Symens et al. 1993, Aspinall 1996, H. King in litt. 2005) since the 1960s, representing a potential loss of up to c.80,000 pairs. In Saudi Arabia, the number of breeding pairs declined by more than 75% during 1980-1992 (Symens et al. 1993). Declines are thought to be continuing due to coastal development, egg and chick collection (Wilson 2012) and marine pollution; and are placed here in the range 30-49% over three generations (c. 26 years).
Phalacrocorax nigrogularis occurs in two subpopulations (Gallagher et al. 1984). The northern one breeds on islands off the Persian Gulf coasts of Bahrain, United Arab Emirates (UAE), Saudi Arabia, Qatar and possibly Iran (breeding not confirmed since 1972) (Gallagher et al. 1984, Symens et al. 1993, Aspinall 1996). The southern subpopulation is apparently much smaller and breeds on one or more islands off the Arabian Sea coast of Oman and in the Gulf of Aden off Yemen (c.60,000 birds in total) (Gallagher et al. 1984, Symens et al. 1993, Aspinall 1996, Jennings 2000). Breeding was confirmed at Socotra for the first time in March 2005, when a colony of c.500 birds was found on the islet of Saboniya (S. Aspinall in litt. 2007), and there is now known to be a population of c.6,250 pairs (Jennings 2010, R. Porter in litt. 2012). There is no evidence of birds moving between the two subpopulations, although this could be taking place (Baha El Din 1991). The overall population is estimated at 110,000 pairs (Jennings 2000) (330,000 [Jennings 2000] to fewer than 500,000 [H. King in litt. 2005] individuals). The species has a very small area of occupancy within its limited breeding range, which has declined rapidly largely because of human disturbance and oil spills (Chiozzi et al. 2007). Only 13 colonies are known to be active at the present time (Symens et al. 1993, Aspinall 1996, H. King in litt. 2005), equivalent to nine locations. The three largest colonies contain at least 75% of the world population (Gallagher et al. 1984, Symens et al. 1993, Aspinall 1996), with that on the island of Suwad al Janubiyah (hereafter Suwad) in the Hawar archipelago being the largest (H. King in litt. 2005). Based on 6 years of study on Siniya Island, it is suggested that the breeding population size fluctuates annually, presumably due to environmental conditions.
In the northern population, c.12 colonies have become extinct (Symens et al. 1993, Aspinall 1996, H. King in litt. 2005) since the 1960s, representing a potential decline of up to c.80,000 pairs (c.26% of the subpopulation). In Saudi Arabia, the number of breeding pairs declined by more than 75% during 1980-1992 (Symens et al. 1993). Only a rare visitor to the Red Sea, with a single individual observed around 1897. It is fairly common along the coast and islands of central and southern Eritrea, particularly in winter, when 500-4,000 birds were observed, and is still present in summer in large numbers (more than 1,500 birds at a time) (Chiozzi et al. 2007). It is suspected to breed off the Danakil coast, although no nesting islands located (Chiozzi et al. 2007).
Behaviour This species is highly gregarious, occurring throughout the year in large aggregations (Johnsgard 1993, King 2004, Nelson et al. 2005). Roosts are tightly packed, occupying the smallest possible ground footprint, potentially to maximise shade to the feet (King 2004). Some seasonal movements are thought to occur, probably related to fish migrations (Symens et al. 1993, Aspinall 1996), where the species travels in large flocks (del Hoyo et al. 1992) within the Persian Gulf and the Arabian Sea. However it is difficult to separate seasonal movements from dispersal (Johnsgard 1993). Socotra Cormorants on Siniya Island outfitted with satellite transmitters exhibit dispersive migration. They fly mostly along the Abu Dhabi coastline towards offshore islands in the area to oversummer (Muzaffar, et al. 2016). In late summer they move across towards the Musandam peninsula to later descend along the northern UAE to Siniya Island in late August. Movement patterns suggest a strong link with oceanographic variables and chlorophyll that is linked to fish productivity and movements. It occurs as a vagrant as far east as west India, and west to the African coast of the Red Sea (del Hoyo et al. 1992). The breeding season is variable with laying recorded in most months, but each colony is internally synchronised (del Hoyo et al. 1992). Breeding has been reported to occur on the Kuria Maria islands from June to October (Gallagher and Woodcock 1980), on Halne Island in the Persian Gulf from January to March (Meinertzhagen 1954), and on the islands off Saudi Arabia in April, May, September, October and November (Bundy et al. 1989). It is suspected that breeding occurs irregularly to in response to locally varying food availability (Johnsgard 1993). Habitat The species is exclusively marine and occurs within the range of productive upwellings (Nelson et al. 2005). Breeding It breeds on offshore islands and islets that have shores of level sand or gravel (del Hoyo et al. 1992). Nonbreeding Outside the breeding season it roosts on coastal cliffs and rocky islets (del Hoyo et al. 1992). Diet Its diet consists principally of small pelagic shoaling fish for which it dives from the surface to depths in excess of 18 m (King 2004). It is regularly seen drowned in fishing traps at various depths (King 2004). Information concerning prey species is scarce (Johnsgard 1993, Nelson et al. 2005) although sardines (Sardinella spp.), scads (Selar crumenophthalmus and Atule mate), Silverside Atherinomorphus lacunosus, Spotted Half-beak Hemiramphus far and Streaked Rabbit-fish Siganus javus are probably among the species taken (King 2004). On Siniya Island, Socotra Cormorants prey on Anchovies (Encrasicholina spp.), Sailfin Flying Fish (Parexocoetus mento), Blue-stripe Sardines (Herklosichthys quadrimaculatus) and a few other species in varying proportions (Muzaffar et al. 2017). It appears that the species is opportunistic in its feeding habits. Perceived competition with fish species targeted in the fisheries is unfounded since there is low overlap between prey species and fisheries landings in the UAE (Muzaffar et al. 2017). Foraging occurs offshore in large groups (Gallagher and Woodcock 1980), and is thought to be communal rather than cooperative (Nelson et al. 2005). One study from Siniya Island suggests that birds use group foraging to detect prey and transmit information (Muzaffar, in litt. 2016). Breeding Site Breeding occurs on shores of level sand or gravel, or gently sloping hills free from vegetation (Johnsgard 1993), since unimpeded access by foot is essential (Aspinall 1996). Nests consist of depressions in the substrate, or in small mounds of substrate, and occur at high densities (Nelson et al. 2005) in colonies that range in size from 50 to tens of thousands of pairs (Johnsgard 1993, Nelson et al. 2005). Nests may be built under planted trees although nesting in open areas is preferred (Muzaffar et al. 2012, Muzaffar et al. 2015).
Coastal development on breeding islands is likely the greatest threat to the species with detrimental effects in the past, present and future (BirdLife International 2010). Frequent human disturbance flushes parenting birds from nests, resulting in widespread egg and chick predation by gulls, Larus spp. (Gallagher et al. 1984, Symens et al. 1993, Aspinall 1996). Total colony abandonment also occurs, and is not always followed by successful relocation elsewhere (Gallagher et al. 1984, Symens et al. 1993, Aspinall 1996). The extinction of 12 colonies since the 1960s is attributed to encroachment by development and prolonged human disturbance (H. King in litt. 2005). A current proposal to build a large multi-use project on Siniya Island (at present supporting a stable colony of c. 25,000 breeding pairs) including a bridge to the mainland, is likely to see the loss of this colony as a result of disturbance and subsequent access to terrestrial predators (S. Muzaffar in litt. 2016).
Parent cormorants tend to respond to threats by departing from the nest rather than defensive aggression, leaving the chicks vulnerable to predation. In 2011, reports suggests that three Feral Cats Felis catus and three Red Foxes Vulpes vulpes were alone responsible for the death of c. 2,000 birds. The island has capacity to sustain far larger predator populations, and there is potential for future increases in predation pressures. Simulated population models under these predation levels predict declines to near-extinction levels (a few hundred individuals) within 30 years (Muzaffar et al. 2013). Predation by gulls, Larus spp. contributes to reduced reproductive success and is exacerbated by human disturbance (Gallagher et al. 1984, Symens et al. 1993, Aspinall 1996).
As a ground-nesting species, it is vulnerable to the effects of storms, such as the flooding of nests during heavy rains, as took place on Suwad in November 1997. Similarly, in April 2003, an isolated thunderstorm with strong winds resulted in sudden termination of breeding and mass abandonment of chicks (H. King in litt. 2005).
The species is highly vulnerable to marine oil spills (Gallagher et al. 1984, Symens and Suhaibani 1993, 1994). In August 1980 an oil spill of about 20,000 barrels off the coast of Bahrain killed up to 1,000 birds, most of which were Socotra Cormorants (Baha El Din 1991). After the 1991 Gulf War oil spill, 82 sites were affected, spanning 200km of coastline between al-Khafji in the north and Jubail in the south. Three months rendered a total count of 10,243 oiled bird carcasses, of which 26% were Socotra Cormorants, representing more than 25% of the species’ Saudi Arabian population (Symens and Suhaibani 1994). Apart from direct mortality, effects include reduced immune function and reduced breeding success from oiling and ingestion, and depletion of prey fish stocks (Baha El Din 1991). As a piscivore, the species is susceptible to other marine pollutants such as heavy metals and PCBs (Polychlorinated biphenyls) as well as neurotoxins (Baha El Din 1991).
The species suffers minor effects from competition with fisheries, including non-targeted capture of prey species or their use as baitfish (Muzaffar et al. 2017). The diet of chicks varied significantly between years, suggesting that the species is a generalist and feeds opportunistically on abundant fish species (Muzaffar et al. 2017). Illegal hunting and egg collection at remaining breeding sites poses a threat of unknown scope.
Conservation Actions Underway
CITES Appendix II. The species is legally protected in most range states (Symens et al. 1993), but not in UAE (Aspinall 1995). Research on the species has increased during the last 10 years, and specific conservation measures have been proposed and acted upon, including the protection of some breeding sites. More surveys are planned by the Eritrean Coastal, Marine and Island Biodiversity project to investigate further evidence of nesting (Chiozzi et al. 2007).
80 cm. Large, blackish cormorant with bronze-green sheen on back and wings. In breeding season, becomes more glossy, with fine, white flecks on neck. Similar spp. Great Cormorant P. carbo is larger, with stouter bill and white face and chin-patch.
Text account compilers
Martin, R., Taylor, J., Ekstrom, J., Capper, D., Miller, E., Pilgrim, J., Anderson, O., Evans, M., Moreno, R., Fjagesund, T.
Contributors
Aspinall, S., Jennings, M., King, H., Porter, R., Muzaffar, S. & Kennedy, M.
Recommended citation
BirdLife International (2024) Species factsheet: Socotra Cormorant Phalacrocorax nigrogularis. Downloaded from
https://datazone.birdlife.org/species/factsheet/socotra-cormorant-phalacrocorax-nigrogularis on 24/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 24/12/2024.