White-headed Duck (Oxyura leucocephala)

Reproduction

The species forms monogamous pair bonds of seasonal duration. The nest is usually located over water in emergent vegetation. Females lay 4-9 eggs, more usually 5 or 6, at 1.5 day intervals, and may relay if the first clutch is removed. Relative to body mass, lays the largest egg of any waterfowl, and total clutch mass may approach 100% of a female’s non-breeding body weight. Incubation begins from April to June in southern Europe, and up to a month later further north. Eggs hatch after 22-24 days in the wild. Only one brood is reared per year. Little information on hatching or nesting success. Brood size at hatching 3-7 ducklings, usually 5-6. The fledging period is 8-10 weeks, somewhat longer than most ducks. Females can breed first at one year old although the proportion doing so is unknown. It is one of the few water birds that moult twice a year, during breeding season and winter, being unable to fly during these periods.

Feeding habits

White-headed Ducks feed almost entirely by diving, mainly at night. Benthic Chironomid larvae are the major diet component at most sites, both for adults and ducklings, but polychaetes (especially in coastal lakes used as wintering sites), amphipods and a variety of other invertebrates are eaten, as well as seeds and vegetative parts of Potamogeton, Ruppia, Scirpus and many other aquatic plants. The availability of chironomid larvae is a key feature in habitat selection. Wintering birds on Caspian Sea contained snails Hydrobia, red seaweed Polysiphonia, and stonewort Chara, and seeds of Ruppia maritima. Females from central Kazakhstan, in July, contained seeds of Potamogeton and Najas, and waterboatmen Corixa and Micronecta. Young caught at same time had only insects.

Video White-headed Duck

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Conservation

Despite uncertainty about the possible large-scale inter-year movement of birds between wintering sites, mid-winter counts indicate that the population of this species has undergone a very rapid decline, which qualifies it as Endangered. The Spanish subpopulation has now stabilised, and it is projected that the global rate of decline will be lower in the next ten years. The species is Palearctic, with a fragmented breeding distribution extending east from Spain and Morocco in western Europe to western China and western Mongolia, and north from Iran to southern Russia. Divisions between biogeographical populations are poorly understood (Scott & Rose 1996), but four major populations are thought to remain: a migratory central Asian population breeding mainly in northern Kazakhstan and southern Russia and wintering in western Asia, the Middle East and in eastern Europe as far west as Greece; a small and declining migratory east Asian population, wintering in Pakistan and perhaps originating from southern Russia and Mongolia; a population resident in Spain, the Spanish population has increased from 22 birds in 1977 to around 2,500 wintering birds today; and another resident in North Africa (Tunisia and north-east Algeria). Most of the population is concentrated in only four countries (Mongolia, Kazakhstan, Russian Federation, and Spain). The most important wintering countries differ from year-to-year, presumably depending on weather conditions. In recent years, ten countries have held over 1,000 birds (Azerbaijan, Bulgaria, Greece, Islamic Republic of Iran, Israel, Kazakhstan, Russian Federation, Spain, Turkey, and Uzbekistan. Seven countries hold significant numbers of White-headed Ducks throughout the year (Algeria, Islamic Republic of Iran, Russian Federation, Spain, Tunisia, Turkey, and Uzbekistan). Since a few years the Spanish population is threatened by hybridisation with the Ruddy Duck, Oxyura jamaicensis, an introduced species from America. The other main threats are over hunting and habitat destrution.