Svasso collorosso

Identificazione

The red-necked grebe is a medium-large grebe, smaller than the great crested grebe of Eurasia, and the western and Clark's grebes of North America, but noticeably larger than other northern grebe species. The adult of the nominate European subspecies is 40–50 cm (16–20 in) long with a 77–85 cm (30–33 in) average wingspan, and weighs 692–925 g (24.4–32.6 oz). In breeding plumage, it has a black cap that extends below the eye, very pale grey cheeks and throat, a rusty red neck, dark grey back and flanks, and white underparts. The eyes are dark brown and the long, pointed bill is black with a yellow base. <p>The winter plumage of the red-necked grebe is duskier than that of other grebes; its dark grey cap is less defined, and merges into the grey face, and a pale crescent that curves around the rear of the face contrasts with the rest of the head. The front of the neck is whitish or light grey, the hind neck is darker grey, and the yellow of the bill is less obvious than in summer. Although the red-necked grebe is unmistakable in breeding plumage, it is less distinctive in winter and can be confused with similar species. It is larger than the Slavonian (horned) grebe, with a relatively larger bill and a grey, rather than white face. It is closer in size to the Eurasian great crested grebe, but that species is longer-necked, has a more contrasting head pattern, and always shows white above the eye.<p>The sexes are similar in appearance, although the male averages heavier than the female. Chicks have a striped head and breast, and older juveniles have a striped face, diffuse blackish cap, pale red neck and extensive yellow on the bill.<p>The subspecies P. g. holboelii is larger than the nominate race at 43–56 cm (17–22 in) length, with a 61–88 cm (24–35 in) wingspan, and a weight of 750–1,600 g (26–56 oz). The plumages are the same as those of the nominate race, although the adult's bill is more extensively yellow. The difference in size between the sexes is greater than for this subspecies that for P. g. grisegena.<p>The red-necked grebe flies with its long neck extended and its large feet trailing behind the body, which gives it a stretched-out appearance. The relatively small wings are grey with white secondaries, and beat very rapidly. Its small wing area means that the grebe is unable to take off from land, and needs a lengthy run across water to gain the speed needed for take-off. Like all grebes, the red-necked is an expert swimmer; it uses its feet for propulsion underwater, and steers by rotating its legs, since its tail is too short for this purpose.<p>This is one of the most vocal grebes during the breeding season, but, like its relatives, it is mainly silent for the rest of the year. It has a loud, wailing or howling display call uooooh, given by a single bird or a pair in duet, by night or during the day, and often from cover. Long sequences of up to 60 consecutive notes may be delivered during singing encounters between rival territorial birds. A great variety of quacking, clucking, hissing, rattling and purring calls are also given, with much individual variation.

Tassonomia

The red-necked grebe was described by the French polymath Georges-Louis Leclerc, Comte de Buffon in 1781 in his Histoire Naturelle des Oiseaux. The bird was also illustrated in a hand-coloured plate engraved by François-Nicolas Martinet in the Planches Enluminées D'Histoire Naturelle which was produced under the supervision of Edme-Louis Daubenton to accompany Buffon's text. Neither the plate caption nor Buffon's description included a scientific name but in 1783 the Dutch naturalist Pieter Boddaert coined the binomial name Colymbus grisegena in his catalogue of the Planches Enluminées. The type locality was subsequently designated as France. The red-necked grebe is now placed in the genus Podiceps that was erected by the English naturalist John Latham in 1787. The genus name Podiceps comes from Latin podicis, "vent" or "anus", and pes, "foot", and is a reference to the placement of a grebe's legs towards the rear of its body. The species name grisegena is from Latin griseus (grey) and gena (cheek) and refers to the face pattern of the breeding adult.<p>Grebes are small to medium-large water birds with lobed, rather than webbed, toes. There are several genera, of which the most widespread is Podiceps with nine species, one recently extinct. The red-necked grebe's closest relative is the fish-eating great crested grebe of Europe and western Asia. It is possible that the red-necked grebe originally evolved in North America and later spread to Europe, where a change of diet to include more insects helped to reduce competition with its larger cousin. Fossils of the species dating to the middle Pleistocene have been found in Italy.<p>The red-necked grebe has two subspecies, the nominate subspecies P. g. grisegena in Europe and western Asia, and P. g. holboelii (Holboell's grebe, named for Danish explorer of Greenlandic birds Carl Peter Holbøll) in North America and eastern Siberia. The east Asian birds have slightly smaller bills than the American form, although the differences are too small to merit separation as a third subspecies.

Nome scientifico

Podiceps grisegena

Autorità

(Boddaert, 1783)

Ordine

Podicipediformes

Famiglia

Podicipedidi

Genere

Podiceps

Areale e habitat

Breeding takes place in shallow freshwater lakes, bays of larger lakes, marshes, and other inland bodies of water, often less than 3 ha (7.4 acres) in extent and less than 2 m (6.6 ft) deep. The red-necked grebe shows a preference for waters in forested areas or, further north, in shrub tundra, and favours sites with abundant emergent vegetation, such as reedbeds. The best breeding habitat is fish-ponds, which have an abundance of food in addition to meeting the other requirements. The American subspecies is less tied to a high aquatic plant density, and sometimes breeds on quite open lakes.<p>All populations are migratory and winter mainly at sea, usually in estuaries and bays, but often well offshore where fish are within diving reach near shallow banks or islands. The preferred passage and wintering habitat is water less than 15 m (49 ft) deep with a sand or gravel bottom, scattered rocks and patches of seaweed. During winter, birds typically feed alone and rarely aggregate into flocks, but on migration, concentrations of over 2000 individuals may occur at favoured staging sites. Migration is usually at night, but may occur during the day, especially when over water. This is particularly noticeable in autumn on the Great Lakes, when up to 18,000 birds may pass Whitefish Point on Lake Superior; these are thought to be Canadian breeders heading for the Atlantic Ocean to winter. This easterly route is longer than that to the Pacific, but avoids the Rockies.<p>The breeding range of the red-necked grebe overlaps with that of the Slavonian grebe, although the latter species tends to be displaced from sites suited to both. The red-necked grebe prefers an inland temperate climate, and is less successful near coasts and in subarctic and warm temperate zones. It is usually a lowland bird, breeding below 100 m (330 ft), although has nested at up to 1,800 m (5,900 ft) in Turkey.<p>The nominate subspecies breeds from southern Sweden and Denmark through central and eastern Europe east to western Siberia, and winters mainly in the North and Baltic Seas, with smaller numbers in the Adriatic, Black Sea, Caspian Sea, Mediterranean and on inland lakes. P. g. holboelii breeds in North America in Alaska, western and central Canada, and the northern US east to Minnesota; in Asia it nests in eastern Siberia from Kamchatka south to Hokkaido and west to Mongolia. The Asian birds winter at sea from Japan to the East China Sea, and American breeders winter in the Pacific, mainly from southern Alaska to British Columbia (with smaller numbers south to California), and in the Atlantic from Newfoundland and Labrador to Florida. Some birds remain on the Great Lakes if they are sufficiently ice-free. This species occurs as a rare winter vagrant in Afghanistan, Pakistan and parts of northern and western India.

Migrazione

Migratori completi

Comportamento

Comportamento migratorio: Migratori completi.

Conservazione

Tendenza della popolazione: in diminuzione.

Tendenza della popolazione

in diminuzione