Justification of Red List Category
This species is not currently declining and is unlikely to decline sufficiently rapidly in the near future to be listed as Near Threatened. It is therefore treated as Least Concern.
Gutiérrez and Guinart (2008) reported a global population of 21,161 pairs. However, more recent figures point to a total of 21,300-22,300 pairs, of which 21,080-21,310 pairs are in Europe. The most recent estimate for the European population is 43,000-44,000 mature individuals (BirdLife International 2015). The global population is estimated to number 63,900-66,900 individuals (G. Eken in litt. 1999, N. Baccetti in litt. 2008, D. Portolou in litt. 2010).
The population has expanded owing to increased availability of fisheries discards close to key breeding colonies. Current fishery practices are unsustainable and may result in collapse in the fishery in the future. This would induce population declines in Audouin's Gull. The European breeding population has increased substantially over the last three generations (39 years, based on a generation length estimated by BirdLife to be 13 years) (BirdLife International 2015). Since 2000, numbers have remained stable overall, with continued increases in some western and central Mediterranean countries, declines in a few eastern Mediterranean countries, and fluctuations in Spain, which holds c. 90% of the European population.
This species breeds in (all data for pairs) Spain (19,461), mainly the Chafarinas Islands and the Ebro Delta with the latter holding 67% of the global population (14,177 in 2007 [Gutiérrez and Guinart 2008]), Algeria (100-600), Greece (350-500), and Sardinia and Tuscan Archipelago, Italy (1,153-1,286), with smaller colonies in Portugal (400-460), Corsica, France (82), Cyprus (14-28), islets and rocks in the southern Adriatic Sea near Korcula and Peljesac Peninsula, Croatia (60-70), Turkey (47-90) (BirdLife International 2015),Tunisia (70-115) and Morocco (50-300). It winters on the coast of North and West Africa from Libya west to Morocco and south to Mauritania, Gambia, Senegal and Gabon (Sanpera et al. 2007) and there is a small wintering population in the east Mediterranean along the Aegean coast of Turkey.
The global population has been estimated at 21,161 pairs (Gutiérrez and Guinart 2008), and a recent assessment estimated the European population (encompassing over 90% of the global population) to be stable or increasing throughout (Barov and Derhé 2011). This represents a significant increase from an estimated population of 1,000 pairs in 1975 and is thought to be a result of the increased availability mainly of effectively protected areas during the 1980s, and secondly of discarded fish from the trawlers, particularly around the Ebro Delta (Criado 1997) where the colony has grown rapidly since 1981 (Guitiérrez and Guinart 2008). The large expansion of this species in the western Mediterranean has probably caused the breeding population in other parts of the Mediterranean to increase and new colonies have been found in Croatia and even out of the Mediterranean in southern Portugal (BirdLife International 2004, Onmus 2006). Nevertheless more than 90% of the European breeding population occurs at just four sites and only a single site (the Ebro Delta) held 67% of the global breeding numbers in 2007. Recruitment can be extremely rapid when food availability is high, resulting in high population growth rates (Oro and Pradel 2000, Tavecchia et al. 2007). It is a long-lived species with high adult survival and relatively low fertility. Adult annual survival is estimated at 0.95 (Oro et al. 1999, 2004, Tavecchia et al. 2007).
Colonies are located on exposed rocky cliffs and on offshore islands or islets, normally not more than 50 m above sea level (Cramp and Simmons 1983). The Ebro delta colony is located on saltmarsh and a sandy peninsula (Olsen and Larsson 2003). In the Aegean it breeds on uninhabited islands sloping gently to the sea and covered with large stones, eryngo Eryngium, grass and low bushes of Pistacia lentiscus (Cramp and Simmons 1983). Characteristics of habitats used differ from region to region and even within the same areas in different years: altitude ranges from close to sea-level to 100 m, vegetation cover from bare rocks to 85% bush cover, and slope from 0-90o. Medium vegetation cover is preferred, and this probably provides chicks with shelter from heat and predators. The concentration of breeding colonies in the western Mediterranean is possibly related to the lower water salinity and higher abundance of clupeids. During the non-breeding season the species prefers sheltered bays, either flat and shingly, sandy or with cliffed margins (Cramp and Simmons 1983). It sometimes visits seaside resorts and marinas lured by food, and it especially likes areas on beaches where freshwater occurs, such as stream mouths or floods (Cramp and Simmons 1983).
It is a coastal species, rarely occurring inland and generally not travelling far offshore (Cramp and Simmons 1983). It was historically thought to feed far out to sea, but more recent observations show that it feeds regularly along the coast. The diet consists mostly of epipelagic fish, especially Clupeiformes, for which it sometimes forages at night, taking advantage of its prey's diurnal vertical (diel) migration patterns (Mañosa et al. 2004) and of commercial fishing by purse-seine netting (Pedrocchi et al. 2002). It is also known to take some aquatic and terrestrial invertebrates, small birds and plant material such as the peanut Arachis, olive Olea, and grain (Cramp and Simmons 1983). The Ebro delta colony feeds largely on fish waste dumped by boats fishing nearby (Oro and Martínez-Vilalta 1992). The species is also known to feed on food discarded at tourist beaches (Cramp and Simmons 1983), and during a moratorium on trawling, it was found to forage in marshes, rice fields and occasionally at refuse tips (del Hoyo et al. 1996, Mañosa et al. 2004). They began to exploit the introduced North American Red Swamp Crayfish Procambarus clarkia, which are abundant in rice fields around the delta (Gutiérrez and Guinart 2008). Hence Ebro Delta birds have developed from being mainly pelagic foragers to more coastal-foraging, even scavenging species (Gutiérrez and Guinart 2008). The fishing moratorium was relaxed in 2000 during the breeding season, and as discards became available, so the population was boosted once again (Gutiérrez and Guinart 2008). Diet during the breeding season has been found to vary between colonies due to fishing practices that target different species in the respective areas (Pedrocchi et al. 2002).
During the non-breeding season, surveys in Morocco found birds no further than 46 km from the coast (Hoogendoorn and Mackrill 1987), and generally <40 km from the colony seems to be the norm (Mañosa et al. 2004). However, the maximum recorded foraging range from a colony was 160 km (Mañosa et al. 2004). In recent years, some birds have remained at the Ebro Delta colony over-winter, with an average of c. 90 birds during 1996-2008, but occasionally up to 300 birds (Gutiérrez and Guinart 2008). The species primarily forages in coastal and continental shelf areas between 5 and 15 nautical miles (nm) offshore. A radius of 15 nm from the Ebro Delta would ensure the protection of 30% of the birds (or 30% of the foraging area). A 30 nm radius would protect 80% of birds. These distances could be reduced in colonies where the surrounding continental shelf is narrower (SEO/BirdLife in litt. 2010). Juveniles tend to forage in upwelling zones, whereas subadults and adults are more independent of these sites (Martinez-Abrain et al 2002). It remains extremely rare along the northern coast of Spain (Gutiérrez and Guinart 2008).
It is partially migratory and dispersive (del Hoyo et al. 1996). It breeds in large monospecific colonies ranging from 10 up to 10,000 pairs (del Hoyo et al. 1996) at a density of up to one nest/ sq. m (del Hoyo et al. 1996) . Egg-laying takes place in the second half of April until the beginning of May, and peak hatching occurs in late May (del Hoyo et al. 1996), with fledging mainly in the first two weeks of July. It has a large foraging range while breeding, and has been recorded up to 200 km from the colony (Mañosa et al. 2004). After breeding the birds disperse widely around the Mediterranean coast (Sanpera et al. 2007; del Hoyo et al. 1996). Almost all juveniles and some adults migrate past Gibraltar during July-October (Olsen and Larsson 2003), peaking in August (Guitiérrez and Guinart 2008), to winter on the North African coast (del Hoyo et al. 1996). During the winter it roosts in flocks of several thousand (Olsen and Larsson 2003). It returns to its breeding sites between late February and mid April (del Hoyo et al. 1996). First year birds remain in the non-breeding range throughout the summer (Cramp and Simmons 1983), while most third-summer birds attend the breeding colony as non-breeders (Gutiérrez and Guinart 2008). Second-summer birds migrate to the Mediterranean but do not join the colony, instead forming large gatherings, often far from colonies (Gutiérrez and Guinart 2008).
Very high colony-site fidelity is probably related to previous breeding success. However, in the Aegean Islands, birds return to the same island group but not necessarily to the same islet. At the Ebro Delta, Spain, c. 1,400 breeders disperse to other colonies every year, generating marked fluctuations at those sites (Tavecchia et al. 2007). The Audouin's Gull is one of the few species of Larid to show nocturnal foraging patterns, which may be linked to fisheries activities; arrivals and departures from the Ebro Delta colony are in accordance with the trawling timetable (Mañosa et al. 2004). The species scavenges around fishing vessels, and uses discards extensively and very efficiently (Mañosa et al. 2004). The species's association with fisheries is more pronounced in the western than in the central and eastern Mediterranean (Pedrocchi et al. 2002), and the trawler moratorium off the Ebro Delta established in 1991 reduced food availability to birds and impacted breeding success, possibly by increasing foraging ranges (Arcos and Oro 1996).
The trawling fishery off the Ebro Delta is regarded as unsustainable and its collapse would probably result in a decline in the breeding population due to the increase in density-dependence (Oro et al. 2004, Tavecchia et al. 2007, Barov and Derhé 2011). A similar outcome would arise if waste from the trawlers were used industrially to produce food for domestic animals, as occurs in other areas, rather than being dumped near the Ebro colony. More important could be the reduction of small-pelagic fish stocks, the main natural prey for Audouin's Gull, due to increasingly high fishing pressure around the breeding grounds, owing partly to high demand by tuna-farming (Arcos et al. 2006). Other important threats include coastal tourism developments, regulation of the river Ebro, mortality due to entanglement in fishing gear (mainly longlines and sporting lines) (Belda and Sánchez 2000, Cooper et al. 2003), and predation by terrestrial predators, such as Red Fox Vulpes vulpes, Earasian Badger Meles meles and domestic dogs (Oro et al. 1999, Tavecchia et al. 2007). Predation by sympatric Yellow-legged Gull L. michahellis can be high at some breeding colonies, especially when densities of Audouin's Gulls are low (Bonaccorsi 2003; Travichon 2004; Oro et al. 2006; Paracuellos and Nevado 2010). Predation on chicks by Black Rats Rattus rattus has a negative impact at some breeding colonies (Jones et al. 2008). Nevertheless Audouin's Gull shows a very nomadic breeding site selection and high dispersal rates from year to year, probably avoiding large densities of Yellow-legged Gulls (Genovart et al. 2003, Martínez-Abraín et al. 2003, Oro and Matínez-Abraín 2007). Peregrines Falco peregrinus, other raptors, some herons and snakes can also prey on adults and nests but only accidentally and locally (Oro 1996, 1997).
Very high levels of mercury and other pollutants are found in this species (Sanpera et al. 2007), partly due to the consumption of discards (Arcos et al. 2002), thus posing a potential threat, although no negative effects have been demonstrated. Current marine wind-farm projects, particularly around the main breeding colony (Ebro Delta), could also represent a serious threat. Overgrazing of some islets by goats in the east of its breeding range may reduce breeding success. Natal and breeding dispersal are extremely high ensuring genetic mixing and buffering against bad local environmental conditions through emigration and colonisation (Oro and Ruxton 2001, Oro et al. 2004).
Conservation and Research Actions Underway
CMS Appendix I and II. A European action plan was published in 1996. The ecology of this species, particularly its breeding and foraging behaviour and demography and population dynamics, has been extensively studied. Lebanon prepared an action plan to restore the breeding population back to Palm Islands Nature reserve. Several LIFE Nature projects have been implemented between 1992 and 2006 in Spain and Italy, contributing to successful recolonisation of breeding islands. There is work underway to introduce best practice measures on board fishing vessels to reduce the incidence of seabird bycatch, however the use of bycatch mitigation gear is not currently widespread in vessels within the Mediterranean, and enforcement is generally very low. Control of invasive black rats Rattus rattus has been effective at some colonies (Jones et al. 2008). Culling of Yellow-legged Gulls Larus michehellis was conducted from 2000 to 2009 on Alborán Island, Spain, and demonstrated immediate local benefits (Paracuellos and Nevado 2010). However, even in small, remote colonies, culling needs to be continuous to avoid a return to the original situation (Paracuellos and Nevado 2010). A LIFE project ran from 2009 to 2012 in Greece, the conservation actions implemented included rat eradication on nine groups of islets supporting over 50% of the species's Greek population and identification of marine IBAs (Fric 2014). In 2014 the species received additional protection when many of its key sites were designated as marine protected areas by Spain – including the area offshore from the Ebro Delta, which is heavily used for feeding by birds from the world’s largest breeding colony (Cantaloube 2014).
Conservation and Research Actions Proposed
Continue to monitor breeding colonies. Identify appropriate actions to mitigate against the key threats. Implement strict fishery management policies in the species's range. Increase the area of suitable coastal habitat that is protected from development and degradation. Enforce laws designed to minimise marine pollution. Implement measures to reduce mortality in fishing gear, perhaps facilitated by legislation. Ensure regulation of the river Ebro benefits the species.
48-52 cm. An elegant medium sized gull with pale grey upperparts. Adult has distinctive bill at close range dark reddish with pale tip unlike any of the larger gulls. Rump, underwing flanks, sides of breast, and hindneck are washed with pale grey, contrasting in good conditions with the whiter head. In flight slight contrast between pale grey upperwing and white trailing edge to the secondaries and strong contrst with black area of the primaries . Winter adult has brownish freckiling on nape and sides of head. Legs dark greyish or greenish and iris dark. Sexes similar. Similar spp. Herring Gull L. argentatus, Lesser Black-backed Gull Larus fuscus (especially juveniles), Yellow-legged Gull Larus cachinnans. L. audouinii Has more elegant appearance with with long, sloping forehead and different facial expression. Legs, bill and iris dark at all ages. Paler grey upperparts than Herring or Yellow-legged Gulls; in flight the wings are slimmer and more pointed and tail appears short narrow. Only one mirror in wingtip compared to usual two in Herring and Yellow-legged Gulls. Voice Typically gull-like and similar to Herring Gull but hoarser and deeper. Hints Scavenges less than other gulls often seen patrolling the sea with steady flight gliding for longer periods than other similar gulls. Will attend fishing boats.
Text account compilers
Anderson, O., Bird, J., Calvert, R., Capper, D., Harding, M., Hatchett, J., O'Brien, A., Peet, N., Pilgrim, J., Derhé, M., Ashpole, J & Tarzia, M
Arcos, J., Carboneras, C., Eken, G., Omnus, O., Oro, D., Papaconstantinou, C., Anderson, O., Portolou, D., Baccetti, N., Hellicar, M., Bourne, W. & Recorbet, B.
BirdLife International (2018) Species factsheet: Larus audouinii. Downloaded from http://www.birdlife.org on 15/08/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 15/08/2018.