Habitat and Ecology
Habitat and Ecology
Behaviour Audouin's Gull is a medium sized gull largely restricted to the Mediterranean. It is partially migratory and dispersive30. It breeds in large monospecific colonies ranging from 10 up to 10,000 pairs30 at a density of up to 1 nest/ sq. m30 . Egg-laying takes place in the second half of April until the beginning of May, and peak hatching occurs in late May30, 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 colony27. After breeding the birds disperse widely around the Mediterranean coast13,30. Almost all juveniles and some adults migrate past Gibraltar during July-October31, to winter on the North African coast30. During the winter it roosts in flocks of several thousand31. It returns to its breeding sites between late February and mid April30. First year birds remain in the non-breeding range throughout the summer32. 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 sites15. 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 timetable27. The species scavenges around fishing vessels, and uses discards extensively and very efficiently27. The species's association with fisheries is more pronounced in the western than in the central and eastern Mediterranean34. A trawler moratorium off the Ebro Delta has caused decreased food availability to birds and has also negatively affected breeding success, possibly by necessitating increased foraging ranges36. Habitat Breeding Colonies are located on exposed rocky cliffs and on offshore islands or islets32, normally not more than 50 m above sea level32. The Ebro delta colony is located on saltmarsh and a sandy peninsula31. 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 lentiscus32. 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. Non-breeding During the non-breeding season the species prefers sheltered bays, either flat and shingly, sandy or with cliffed margins32. 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 floods32. It is a coastal species, rarely occurring inland and generally not travelling far offshore32. Diet This species 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 diel migration patterns27 and of commercial fishing by purse-seine netting34. It is also known to take some aquatic and terrestrial invertebrates, small birds and plant material such as the peanut Arachis, olive Olea, and grain32. The Ebro delta colony feeds largely on fish waste dumped by boats fishing nearby33. The species is also known to feed on food discarded at tourist beaches32, and during a moratorium on trawling, it was found to forage in marshes, rice fields and occasionally at refuse tips27,30. Diet during the breeding season has been found to vary between colonies due to fishing practices that target different species in the respective areas34. Breeding site The nests is a shallow scrape lined with available debris and vegetation32. It is placed among rocks and vegetation30. Foraging range During the non-breeding season, surveys in Morocco found birds no further than 46 km from the coast37, and generally <40 km from the colony seems to be the norm27. However, the maximum recorded foraging range from a colony was 160 km27. 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 narrower38. Juveniles tend to forage in upwelling zones, whereas subadults and adults are more independent of these sites39.
No one has provided updates yet.