Sunday, October 27, 2013

Megapode - Incubator Bird

The megapodes, also known as incubator birds or mound-builders, are stocky, medium-large chicken-like birds with small heads and large feet in the family Megapodiidae. Their name literally means "large foot" (Greek: mega = large, poda = foot), and is a reference to the heavy legs and feet typical of these terrestrial birds. All are browsers, all but the Malleefowl occupy wooded habitats, and most are brown or black colored. Megapodes are superprecocial, hatching from their eggs in the most mature condition of any birds. They hatch with open eyes, bodily coordination and strength, full wing feathers and downy body feathers,and are able to run, pursue prey, and, in some species, fly on the same day they hatch.

Megapodes are medium-sized to large terrestrial birds with large legs and feet with sharp claws. They range from 28 to 70 cm. The largest members of the clade are the species of Alectura and Talegalla. The smallest are the Micronesian Scrubfowl (Megapodius laperouse) and the Moluccan Scrubfowl (Eulipoa wallacei). They have small heads, short beaks, and rounded and large wings. Their flying abilities vary within the clade. They present the hallux at the same level of the others toes just like the species of the clade Cracidae. The other Galliformes have their halluces raised above the level of the front toes.

Distribution and habitat
Australian Brushturkey
Megapodes are found in the broader Australasian region, including islands in the western Pacific, Australia, New Guinea, and the islands of Indonesia east of the Wallace Line, but also the Andaman and Nicobar Islands in the Bay of Bengal. The distribution of the family has contracted in the Pacific with the arrival of humans, and a number of island groups such as Fiji, Tonga, and New Caledonia have lost many or all of their species.

Behaviour and Ecology
Australian Brushturkey on its mound
Megapodes are mainly solitary birds that do not incubate their eggs with their body heat as other birds do, but bury them. Their eggs are unique in having a large yolk, making up 50-70% of the egg weight. They are best known for building massive nest-mounds of decaying vegetation, which the male attends, adding or removing litter to regulate the internal heat while the eggs hatch. However, some bury their eggs in other ways; there are burrow-nesters which use geothermal heat, and others which simply rely on the heat of the sun warming sand. Some species vary their incubation strategy depending on the local environment. Although the Australian Brushturkey was thought to exhibit Temperature-dependent sex determination it was later proven false, it was speculated that this is common to all Megapodes, as they share nesting methods unique among birds. The non-social nature of their incubation raises questions as to how the hatchlings come to recognise other members of their species, which is due to imprinting in other members of the order Galliformes. Recent research suggests an instinctive visual recognition of specific movement patterns is made by the individual species of megapode.
This cross-section of a megapode mound shows a layer of sand (up to 1 m thick) used for insulation, an egg chamber, and a layer of rotting compost. The egg chamber is kept at a constant 33°C by opening and closing air vents in the insulation layer, while heat comes from the compost below.
Megapode chicks do not have an egg tooth; they use their powerful claws to break out of the egg, and then tunnel their way up to the surface of the mound, lying on their backs and scratching at the sand and vegetable matter. Similar to other superprecocial birds, they hatch fully feathered and active, already able to fly and live independently from their parents.

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