White-headed Duck (Oxyura leucocephala)
spanwidth min.: 64 cm
spanwidth max.: 68 cm
size min.: 43 cm
size max.: 48 cm
incubation min.: 25 days
incubation max.: 26 days
fledging min.: 0 days
fledging max.: 0 days
eggs min.: 5
eggs max.: 12
Chestnut-brown diving duck with long tail, often cocked vertically. Male has white head, black cap and blue bill, swollen at base. Female has pale face with dark cap and cheek-stripe and blackish, less swollen bill. Similar spp. Ruddy Duck O. jamaicensis is smaller with brighter chestnut plumage. Male has more extensive black cap and dark hindneck and female has narrower facial band and browner cap. Both sexes lack swollen base to bill. Hybrid identification can be very problematic. Voice Low rattling noise uttered during display. Otherwise generally silent.
White-headed Ducks breed in shallow fresh or brackish marshes connected with larger wetland complexes. Such wetlands are often seasonal, created by spring floods and drained at summer, but they are especially productive, being very rich in aquatic vegetation and invertebrates. In winter, White-headed Ducks prefer large brackish or saline lakes.
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.
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.
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 of over 50% in the last 10 years, which qualifies it as Endangered. Given increases in the Spanish subpopulation, it is projected that the overall rate of decline will be lower in the next 10 years. [conservation status from birdlife.org]
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.
Resident and dispersive in west Mediterranean. Mainly migratory in east Mediterranean and Asia. The western population is resident, numbering about 1,000 birds breeding mainly in Spain but also in Algeria and Tunisia. The eastern population is larger and migratory. White-headed Ducks breed mainly in Turkey, where the biggest eastern population is located (200-300 pairs), while fewer breed in Russia, Iran and occasionally in Romania.
Moult movements are poorly understood, but large flocks of moulting individuals gather on certain sites (e.g. the Sudochie wetlands in Uzbekistan, and Lake Tengiz in Kazakhstan). Departure from breeding localities begins in late August and is completed by mid-October. In Central Kazakhstan, largest numbers occur in September, but birds leave the region completely by mid-October. In Uzbekistan, major passage through the Amu Darya delta in October. In Pakistan, birds first appear in October and leave by the end of March. It is currently unknown whether there is interchange between the Spanish and North African populations. However, the recent increase in the number of White-headed Ducks in Morocco suggests that interchange does occur. Emigration of birds from Algeria or Tunisia was suggested as a possible explanation for the peak count of 4,489 birds in Spain in September 2002. However, as over 1,000 ducklings were hatched at El Hondo that year, it seems equally likely that these numbers could be explained by a bumper breeding year.