GREBE

Slavonian, or horned, grebe (Podiceps auritus) order name Podicipediformes, member of an order of diving birds containing a single family, Podicipedidae, with about 20 species. Grebes have a pointed bill, short, narrow wings, and a vestigial tail. Their legs, set at the rear of the body, make walking awkward. The wing feathers are curved to fit the back when closed, and the long, partially webbed toes are lobed at the ends. Many grebes have bright, erectile ear tufts and crests in summer but are dully garbed in winter; sexes look alike at all seasons. Grebes feed chiefly on fish or invertebrates. Courting or rival birds perform elaborate aquatic dances in pairs. The nest, a floating mat of plant matter anchored to reeds, may have 2-8 chalky eggs, which become discoloured during the 20-30-day incubation period. Both parents participate in the incubation process. The young of most species are brightly striped. Grebes are found in most tropical and temperate areas and often in subarctic regions. The Palaearctic little grebe, or dabchick (Tachybaptus ruficollis), is one of the smaller grebes, reaching a length of only about 25.5 cm (10 inches). The larger forms, which are also the most notable dancers, include the 48-centimetre (19-inch) great crested grebe (Podiceps cristatus), of the Old World and Australia, and the 70-centimetre (28-inch) western grebe (Aechmophorus occidentalis), of North and Central America, unique as the only grebe that spears its fish prey. Most grebes can fly, and some species are migratory; there are, however, a few Neotropical species that are flightless and limited in range to isolated bodies of water. These are Taczanowsky's, or Puna, grebe (P. taczanowskii), the short-winged grebe (Rollandia, or Centropelma, micropterum), and the giant pied-billed, or Atitlan, grebe (Podilymbus gigas). Slavonian, or horned, grebe (Podiceps auritus) (order Podicipediformes), member of an order of foot-propelled diving birds (see photograph) containing a single family, Podicipedidae, with about 18 species. They are best known for the striking courtship displays of some species and for the silky plumage of the underparts, which formerly was much used in millinery. The speed with which grebes can submerge has earned them such names as water-witch and helldiver, while the position of the feet near the tail is responsible for the early English name arsefoot, from which the family name was derived. Adult grebes range in weight from less than 150 grams (five ounces) to more than 1.4 kilograms (approximately three pounds) and in total length from 21 to 73 centimetres (eight to 29 inches). They vary principally in bill shape and ornamentation of the head. The group is found on all of the continents and on many island groups as well. However, it is best represented in temperate regions. Seven species each are found in North and South America, five in Eurasia, and three each in Africa and Australia. The species range from conspicuous and gregarious to solitary and skulking. Additional reading K.E.L. Simmons, "Studies on Great Crested Grebes," The Avicultural Magazine, 61:3-13, 93-102, 131-146, 181-201, 235-253, 294-316 (1955), is a classic study of grebe behaviour. Several articles by the same author are instructive: R.W. Storer, "The Behavior of the Horned Grebe in Spring," Condor, 71:180-205 (1969), containing comparative material on several species, "The Patterns of Downy Grebes," Condor, 69:469-478 (1967), concerning the colour patterns of grebe chicks, "Courtship and Mating Behavior and the Phylogeny of the Grebes," Proceedings of the XIII International Ornithological Congress (1963), pp. 562-569, and "Evolution in the Diving Birds," Proceedings of the XII International Ornithological Congress (1960), pp. 694-707, providing insight into the evolution and classification of grebes. Robert W. Storer The Editors of the Encyclopdia Britannica