Habitat and Ecology
Habitat and Ecology
Behaviour This species is fully migratory1 although its movements are poorly understood5. It breeds from late-May onwards3 in single pairs or loose groups1, 2, the males leaving the females soon after the start of incubation3 (between late-June and early-September) to gather in small flocks for a flightless moulting period5. Some populations undergo extensive moult migrations of up to 1,000 km, while others moult on waters near the breeding grounds3. Females moult between early-August and early-October on the breeding grounds5, often abandoning their young at the start of the moult (the ducklings then gather into large parentless groups)4. The southward autumn migration occurs from September to October after the post-breeding moult5 and non-breeders may oversummer in the wintering areas3. Outside of the breeding season the species is highly gregarious4, in winter gathering into large aggregations of perhaps several tens of thousands of individuals to roost or to feed in inshore and offshore waters1. The species regularly dives to depths of 3-10 m when foraging (maximum depth 50-60 m)2 and is diurnal2. Habitat Breeding The species breeds on marshy grass tundra in the high Arctic1, 6, especially where habitat mosaics are formed by hummocks and ridges together with moist depressions7, freshwater lakes1, 2, bogs1, slow rivers1, 3 or pools of standing water7. It generally avoids wooded tundra4, 7 but is common among willows or dwarf birch in the arctic-alpine zone (Scandinavia)7. The species also breeds on small rocky islands off mainland Arctic coasts and on larger offshore islands, using promontories, deltas7, coastal inlets1, 3 and islets in fjords (Greenland)7. Non-breeding The species winters at sea, generally far offshore1 in waters 10-35 m deep5, as well as in saline, brackish or fresh estuarine waters4, brackish lagoons1, and inland (very rarely) on large, deep freshwater lakes1. Diet The species showing a preference for marine foods during both the breeding and non-breeding seasons4, its diet consisting predominantly of animal matter7 such as crustaceans1 (e.g. amphipods2 and cladocerans4), molluscs, other marine invertebrates (e.g. echinoderms, worms) and fish1. The species also takes freshwater insects and insect larvae1 as well as plant material such as algae, grasses, and the seeds and fruits of tundra plants1. Breeding site The nest is a natural depression on dry ground positioned in the open, amongst vegetation1, partially hidden by overhanging boulders3 or under low shrubs4 (e.g. willows or dwarf birch)6 usually close to water3. Although it is not a colonial species some pairs may nest in loose groups, and the species may also nest in association with Artic Terns2.
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