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The Dolphin Gull is a Patagonian endemic distributed in the temperate and sub-Antarctic coastline of Chile, Tierra del Fuego and Argentina. It is found along rocky coastline often in the vicinity of fresh water, seabird and marine mammal colonies, slaughterhouses, farmyards and even sewers. Though it could be confused with the two other dark-backed gulls found in its range, Band-tailed and Kelp, its obvious bright red bulbous bill and dusky grey head and underparts make it quite distinctive. Its juvenile plumage is also unique among gulls having a dark gray hood, whitish belly and slaty-brown wing coverts. Its main source of food is scavenged carrion, bird eggs and chicks, other marine invertebrates. It can often be found scavenging around marine mammals for dead fish, placentae, and in particular, feces.
40–46 cm; 524 g; wingspan 104–110 cm. Uniquely plumaged gull , with uniform grey suffusion on head and underbody, dark mantle and black primaries, the latter with no white windows, and broad white triangular trailing edge to secondaries and inner primaries; tail white; heavy bill and shortish legs startlingly bright red ; iris white, with conspicuous red orbital ring. Distinguished from Larus belcheri, which shares some of the same features, by smaller size, lack of black tail band, and noticeably different bare part colours. Non-breeding adult and second-winter bird have a darker grey-mottled hood . Juvenile unique among gulls, uniform dark brown with whitish belly and slaty-brown wing-coverts.
S South America from SC Chile (Chiloé I) and SC Argentina (Punta Tombo, in Chubut) to Tierra del Fuego; also Falkland Is. Outside breeding season, occurs slightly farther N on both mainland coasts.
Falklands population resident, but adults and young disperse widely around the islands. Populations from mainland South America move north, Chilean birds as far as Santa María I; Punta Tombo birds attend sea lion colonies 200 km to the north, on the Valdés Peninsula. Has occurred on South Georgia, presumably as a vagrant (1).
Diet and Foraging
Mainly carrion, offal, bird eggs and chicks; marine invertebrates , and other natural food. Scavenges around marine mammals for dead fish, placentae and particularly faeces; natural foods are taken mostly early in season, before bird eggs available. A radiotelemetric study of foraging birds from the Punta Tombo Reserve colony, Argentina, has shown that these all foraged quite close to the colony during both the incubation and chick rearing stages; and mainly at the colonies of three other species, feeding on Magellanic Penguin Spheniscus magellanicus and Imperial Cormorant Phalacrocorax atriceps regurgitates and on Southern Sea Lion Otaria flavescens faeces (2).
Exploits human intrusion into seabird colonies by preying on unguarded eggs and chicks. Occasionally steals food being delivered to cormorant (Phalacrocorax) and penguin chicks, and pirates stolen penguin eggs from Larus dominicanus. Chicks fed mainly on fish scavenged from around penguin nests. Probes in seaweed; captures swarming beach flies; picks mussels, which are then dropped onto rocks . Some frequent dumps at fish processing works dumps. Also sometimes feeds at sewage outlets. A pellet analysis at a colony in southern Patagonia reveals that the diet includes a diversity of marine molluscs, crustaceans and fish, especially including the mussel Perumytilus purpuratus, the Argentine Hake Merluccius hubbsi and the Patagonian Squid Loligo gahi, but it is unclear to what extent these are secondary prey derived from mammalian faeces (3).
Sounds and Vocal Behavior
Long-call is a combination of guttural chatters and one or two high-pitched piercing screams. Other calls include loud grating notes, singly or in series, high-pitched squeals and subdued “chuk” notes.
Attends colonies from September, laying sometimes in early November (Tierra del Fuego) or late November (Punta Tombo), but mostly in December; highly asynchronous. Changes location from year to year. Nests chiefly in small, dense colonies (1–1·6 pairs/m²) of up to 25 pairs; exceptionally 200+ pairs. Nest of kelp and vegetation, lined with grass; among boulders, or on bare volcanic rock (Punta Tombo), often sheltered by tussock grass. Lays 2–3 eggs (mean 1·9–2·0 Punta Tombo); incubation 24–27 days; tolerates intruders within 1 m of nest, but once flushed will attack; chick is the most boldly marked of any gull, with discrete black spots and streaks forming long bars from gape to below eye, on a very pale ground colour; mean hatching weight 41 g; at 2–5 days follows parents from nest; older chicks may form a crèche. Hatching success c. 50%; remainder of eggs presumably lost to predators. (4)
Not globally threatened (Least Concern). The total population is estimated at 10,000–28,000 individuals Birdlife Datazone . Most of the global population inhabits the Falkland Islands, where there are numerous small colonies totalling 3000–6000 pairs (5). There are many small colonies on the South American coast, where the species is considered common in S Chile and on much of Tierra del Fuego. Most Patagonian colonies support fewer than 25 pairs and the total Argentinian population has been estimated at only 700 pairs in 26 colonies Birdlife Datazone . Populations are considered to be at least stable. The two colonies in the Beagle Channel, Tierra del Fuego, have increased by 5% post-2000, to reach a total of 455 pairs in 2011 (6).