Habitat and Ecology
Habitat and Ecology
Behaviour This species is fully migratory1. It breeds in the high Arctic from late-May or early-June (depending on the timing of the Arctic thaw)2 in single pairs or loose groups1, often with colonies of nesting gulls or terns2 although it is not itself a colonial species6. Males undergo short post-breeding moult migrations3, 5, often gathering in small or large flocks (up to 4,000 in Iceland)5 while females are incubating3. Females usually moult on the breeding grounds3, 5, although large concentrations (500-1,000 individuals) of moulting females have been recorded away from breeding areas5. During the moulting period the species is flightless for a period of c.3-4 weeks5. The autumn migration begins after the moulting period in mid-August5, with males tending to remain much further north than females or immatures1 leading to some sexual segregation during the winter3. The species is highly gregarious outside of the breeding season2 and is commonly observed in small or large flocks3 sometimes of several thousand individuals5. The return spring migration generally begins in late-February5 although flocks of non-breeders may remain in the south, often in winter quarters, during the breeding season3. Habitat Breeding The species breeds in tundra2, wooded tundra5 and moorland regions2 in the high Arctic1, occupying small, shallow1, freshwater lakes, pools and rivers2 with grassy shorelines and high densities of invertebrate life4. It shows a preference for water less than 6 m deep (usually 2 m) for diving2. Non-breeding The species winters on shallow coastal waters1, 2 less than 10 m deep5 (especially in the vicinity of sewage outlets)1, as well as sheltered bays1, estuaries1, 2 and brackish coastal lagoons1. It is also found inland on large lakes1, 2, 4 and reservoirs during this season3. Diet The species is omnivorous2, its diet consisting predominantly of molluscs (e.g. mussels2 Mytilus spp.1, cockles Cardium spp. and clams Macoma spp. in coastal habitats, and Hydrobia spp. in brackish habitats2) especially during the winter4, as well as insects1, aquatic insect larvae4, crustaceans1 (e.g. amphipods4), worms, small fish1, and the roots, seeds and vegetative parts of aquatic plants such as sedges1, 2 and water weeds2. Breeding site The nest is a shallow depression close to water3 on the ground1, either in thick vegetation1, 2, in cracks in rocks, under woody shrubs or under perennial herbaceous vegetation less than 50 cm high (Iceland)4. The species is not colonial but it will sometimes nest among gulls and terns2, with neighbouring nests being placed as close as 1 m in some areas6. Management information In Scotland, UK the introduction of a sewage treatment scheme in the Firth of Forth (a large marine bay) resulted in a considerable reduction in the abundance of the species, with feeding flocks only remaining at outfalls where sewage continued to be discharged in large quantities13. It was unclear whether the changes in the species's distribution were due to reductions in the number of food items borne in the sewage or to reductions in aquatic invertebrate abundance as a result of the new treatment system13.
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