In the 1970s, Audouin’s gull (Larus audouinii) was considered to be the world’s rarest gull, and the species’ unfavourable conservation status prompted widespread concern about its continuing prospects for survival. By 1975, it was estimated that only 1,000 pairs remained in the world. Although the global population increased to an estimated 22,700 pairs by 2010, its population is once again declining and the species has been classified as Near Threatened by the International Union for Conservation of Nature (IUCN) in its 2010 Red List of Threatened Species.
While the 2011-2015 EU LIFE+ Nature project on Andros Island, Greece, endeavours to ensure the continued presence and well-being of Audouin’s gulls along the coasts and azure sea surrounding Andros Island and its islets, these graceful gulls contribute to the island’s productive coastal ecosystems and the island’s long-standing popularity with Greek mainland residents and visitors.
Audouin’s gull is a sleek and graceful seabird with feathers coloured in shades of white, gray and black that are usually associated with gulls, but its striking scarlet red bill that pales at the tip readily distinguishes Audouin’s gull from other gull species.
Audouin’s gull is a medium-sized gull approximately 46-52 centimetres (cm) in length with a 117-128 cm wingspan. This gull features dark eyes, a long sloping forehead, a white head and body with soft pale gray shades appearing on its upper body, dark greenish-gray legs and pale gray wings with black tips and long feathers that cover part of its black tail. In flight, black feathered wedges are visible on the forewing, and the wings are slimmer and more pointed than the Herring Gull (Larus argentatus) or Yellow Legged Gull (Larus michahelis), which are two gull species for which Audouin’s gull is sometimes mistaken. Juveniles are recognisable by their brown heads that fade to white as the bird matures with age.
In steady flight, Audouin’s gull can be observed gliding for longer periods than other similar gulls. Under natural conditions, these gulls are a long-lived species with a high adult survival rate but a relatively low fertility rate.
Audouin’s gull is endemic to the Mediterranean region where the gulls primarily breed in Spain, mainly in the Chafarinas Islands and the Ebro Delta – the latter of which hosted 70% of the global breeding population in just one colony in 2006; Greece; Algeria; and the Sardinian and Tuscan Archipelago (Italy). There are also small breeding colonies in Portugal; Corsica (France); Cyprus; Croatia, especially on islets and rocks near Korcula Island and Peljesac Peninsula in the Adriatic Sea; Turkey; Tunisia and Morocco.
Audouin’s gull winters off the north and west coasts of Africa from Libya west to Morocco and south to Mauritania, Gambia, Senegal and Gabon, and there is also a small wintering population in the eastern Mediterranean along the Aegean coast of Turkey.
Audouin’s gull is a coastal species rarely occurring inland and generally not found very far offshore. They like areas on beaches where fresh water occurs from floods or at the mouths of streams and rivers. The Atlantic and western Mediterranean breeding colonies live by sea water that (i) is less salty than the sea water in the central and eastern Mediterranean and (ii) hosts a higher abundance of clupeids which are primarily marine forage fish preyed on by larger predators including seabirds, larger fish and marine mammals. Clupeids, on which Audouin’s gulls prey, are a family of species (Clupeidae) that usually live in large shoals and include herrings, shads, sardines, hilsa and menhadens.
In the 1970’s, Audouin’s gull was one of the world’s rarest gulls with its population identified as critically endangered; however, since then, the global population has recovered with an estimated 22,700 breeding pairs in 2010. The population increase has been attributed to the establishment of effectively protected areas and a significant amount of discarded fish from trawlers providing foraging opportunities for the gulls, especially in the Ebro Delta region.
In Greece, the Audouin’s gull population increased from just 40 pairs in the 1970’s to 700-900 pairs by the 1990’s; thereafter, however, the Hellenic breeding population experienced a reversal with the population dipping to 400-500 pairs due to a deterioration of the species’ breeding and foraging habitats according to a 2010 species population census.
The EU Andros LIFE+ Nature project area hosts 25-30 pairs of Audouin’s gulls representing 6-7.5% of the national breeding population which are the subject of conservation actions that are designed to improve the gulls’ breeding, foraging and roosting habitats.
Audouin’s gulls were once believed to forage far out at sea, but it is now known that they usually forage along coastal and continental shelf areas with juveniles tending to forage in upwelling zones more than adults. In Greece, for example, Posidonia seagrass beds (Posidonia oceanica), which generally inhabit shallow depths to 30-40 metres, represent a primary foraging habitat for Audouin’s gulls because the seagrass serves as an enriching habitat with plentiful food sources for the natural behaviour and protection of at least 700 animal species and 200 other plant species. In particular, Posidonia beds are especially valued as nursery grounds for a variety of fish and crustacean species that heavily rely on Posidonia for their growth, survival and reproduction.
Along these foraging areas in which Audouin’s gulls exhibit an expansive foraging range – especially during the breeding season when the range can extend as far as 200 kilometres from the colony, the gulls target their main natural prey which consists of small coastal and pelagic fish species as well as other marine organisms that live in shallow coastal waters. The gulls’ prey includes bogues which are a species of seabream (Boops boops), Mediterranean chromis (Chromis chromis), mullets (Mugil spp.) and picarels (Spicara spp.).
The gulls also prey on species belonging to the genus Clupeidae. These fish species are often termed marine forage fish because they are preyed upon by larger predators including larger fish, seabirds and marine mammals. Clupeids, which usually live in shoals, include herrings, sardines, shads, hilsa and menhadens. Common foraging techniques used by Audouin’s gulls include snatching their prey from the near surface of the water while in flight and plunge diving.
Audouin’s gull is one of the few gull species that forage at night as well as in the daytime which may be linked to the diel (24 hour) migration patterns of its prey as well as fishery activities as Audouin’s gulls are often seen in the vicinity of fishing boats; however, the species’ reliance upon fisheries for foraging opportunities - including fishery discards, baited fishing lines and remnants from fish captures in fishing gear - is greater in the western Mediterranean than in the central and eastern Mediterranean. As an example, Audouin’s gull arrivals and departures from the Spanish Ebro Delta colony coincide with fishing trawler timetables.
The Audouin’s gull diet also includes invertebrates such as cephalopods and crustaceans, small birds including passerine migrants and plant material such as peanuts (Arachis hypogaea), olives (Olea europaea) and grain. In the event of insufficient natural prey on which these gulls have traditionally foraged, Audouin’s gulls have resorted to feeding on food discarded at tourist beaches, marinas and waste dumps which is not recommended for their health as well as on sustenance or prey in fields and marshes, including insects and small mammals.
Breeding and Habitat:
Audouin’s gulls breed in colonies that are located in secluded areas on exposed rocky cliffs and on islands as well as islets at low altitudes that do not generally exceed 50 metres. In the Aegean Sea, the gulls breed on uninhabited islands and islets which host rocky habitats that are characterised by plants that ideally provide medium coverage to shelter the eggs and young from predators and strong sun. Vegetation commonly found in these areas includes plants belonging to the genus Eryngium that is commonly known as Sea Holly when applied to coastal species (or Eryngo when applied to grassland species), grass and evergreen Mastic shrubs (Pistacia lentiscus) that can grow to 3-4 metres in height. By contrast, the predominant Spanish Ebro Delta breeding colony is located on a saltmarsh and sandy peninsula.
It must be noted, however, that from year to year, breeding habitat characteristics that are selected by Audouin’s gulls can differ from region to region or even differ within the same geographical areas. For example, the altitude of breeding colonies can range from close to sea level to 100 metres, the cover can vary from exposed rocks to 85% vegetation cover and even the slope can vary from 0 to 90 degrees.
Audouin’s gulls arrive at the nesting colonies every year between March and early April so that by mid to late April the birds have occupied their nesting sites. While the breeding pairs, which are known to be monogamous for at least several years, usually return to the same nesting colony each year, the pairs may use different nesting sites depending on the reproductive success of the clutches during the previous year. In the Aegean Sea, however, the gulls’ breeding site fidelity may only extend to the same island group but not necessarily the same colony. Throughout their entire breeding distribution, colonies range in size from a few pairs to several thousand pairs. In Greece, colony sizes which currently range from 3 to 86 pairs in 28 known locations are considered to be small compared to those in the western Mediterranean.
The Audouin’s gull nest situated among rocks and vegetation consists of a shallow scrape which is formed by lining a shallow depression with small stones or pebbles, shell fragments, bits of plant material such as grasses and leaves and/or feathers. Between late April and early May, the female lays 2-3 eggs and incubates them for three weeks. The peak egg-hatching period occurs in late May. The chicks fledge in early to mid-July when both adults and the young leave the breeding colony and disperse widely along the Mediterranean coast, favouring the North African coast for their wintering grounds. During the non-breeding season, the gulls prefer sheltered sandy or rocky bays that may be situated in flat terrain or with nearby cliffs.
Despite its recent population recovery since the 1970s when Audouin’s gull was the world’s rarest gull, the Audouin’s gull population is currently declining according to the International Union for Conservation of Nature (IUCN). The reasons for its decline include the following threats which are adversely impacting the gulls’ breeding and foraging success which, in turn, affects their conservation status:
- insufficient natural prey caused by the reduction in small pelagic fish stocks, which represent Audouin’s gulls’ main natural prey, due to intensive fishing pressure in the region of the gulls’ breeding grounds. This fishing pressure is attributable to (a) the extraction of fish stocks to supply tuna farms and (b) the absence of sustainable fisheries management in Europe that currently allows overfishing of depleted fish stocks and the fisheries’ overboard discard of tons of unwanted fish every year;
- ingestion of pollutants (e.g. dioxins, organochlorines and heavy metals such as mercury, lead and cadmium) from sources such as (a) pesticides, household waste and industrial waste run-off and (b) the absence of adequate municipal waste management services in coastal communities and islands, such as on Andros Island, which results in coastal marine pollution caused by the release of toxic compounds from the waste that reaches the sea, and many of these compounds represent persistent sources of contamination as they do not readily break down in the terrestrial and marine environment;
- food competition and predation of eggs and chicks at breeding colonies by Yellow-legged gulls (Larus michahellis), predation of eggs and chicks by Black rats (Rattus rattus) especially at island breeding colonies, and predation by other terrestrial species such as red foxes (Vulpes vulpes), badgers (Meles meles) and domestic dogs. To a much lesser extent and on a localised and occasionally accidental basis, predation on adults and nests by Peregrine falcons (Falco peregrinus), other raptors, some herons and snakes also occurs;
- mortality from entanglement in fishing gear, such as baited long-lines;
- coastal development which results in habitat destruction, degradation and/or fragmentation;
- tourism, especially as the Mediterranean tourism season overlaps with the gulls’ breeding season resulting in significant disturbances from terrestrial as well as marine recreational activities;
- overgrazing on islands and islets by goats, especially in the eastern Mediterranean, which can adversely impact breeding success.
The EU LIFE+ Nature project has been designed in part to improve the quality of the Audouin’s gull breeding, foraging and roosting sites in an effort to mitigate the threats with which the gulls are currently faced and thereby improve their long term conservation status.
Laws and conventions related to the status and protection of Audouin’s gull include:
- European Union Birds Directive (2009/147/EC), Annex I;
- Agreement on the Conservation of African-Eurasian Migratory Water Birds (AEWA), Annex II;
- Bern Convention on the Conservation of European Wildlife and Natural Habitats, Appendix II;
- Bonn Convention on the Conservation of Migratory Species of Wild Animals, Appendices I and II;
- International Union for Conservation of Nature Red List of Threatened Species, in which Audouin’s Gull was listed as Near Threatened in 2010 with a declining population;
- Hellenic Ministerial Decision 414985/85 as the Greeks have listed the species as Endangered in the Greek Red Book of Threatened Vertebrates; and
- Species of European Conservation Concern by BirdLife International in which Audouin’s Gull is listed as a SPEC I: globally threatened species endemic to Europe.
Contact: Constantine Alexander
copyright © 2012 Constantine Alexander