Megapode

Megapodiidae
Australian brushturkey (Alectura lathami)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Galliformes
Family: Megapodiidae
Lesson, 1831
Genera

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, and all but the malleefowl occupy wooded habitats. 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.[1]

Description

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 other toes just like the species of the clade Cracidae. The other Galliformes have their halluces raised above the level of the front toes.[2]

Distribution and habitat

Brushturkeys can often be found in parks or gardens.

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.[3]

Behaviour and ecology

Australian brushturkey on its mound
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.

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.[4] 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.[3] Although the Australian brushturkey was thought to exhibit temperature-dependent sex determination, this was later proven false;[5] temperature does, however, affect embryo mortality and resulting offspring sex ratios. 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.[6]

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.[4]

Eggs previously assigned to Genyornis have been reassigned to giant megapode species. A lot of the dietary and chronological data previously assigned to dromornithids may instead be conssigned to giant megapodes.[7]

Species

The more than 20 species are in seven genera. Although the evolutionary relationships between the Megapodiidae are especially uncertain, the morphological groups are clear:[8]

Megapodiidae

References

  1. ↑ Starck, J.M., Ricklefs, R.E. (1998). Avian Growth and Development. Evolution within the altricial precocial spectrum. New York: Oxford University Press. ISBN 0-19-510608-3.
  2. ↑ del Hoyo, J.; Elliott, A.; Sargatal, J. (1994). Handbook of the Birds of the World. Volume 2: New World Vultures to Guineafowl. Lynx Edicions. ISBN 84-87334-15-6.
  3. 1 2 Steadman D, (2006). Extinction and Biogeography in Tropical Pacific Birds, University of Chicago Press. ISBN 978-0-226-77142-7
  4. 1 2 Starck, J.M. & Sutter E. (2000). Patterns of growth and heterochrony in moundbuilders (MEgapodiidae) and fowl (Phasianidae). Copenhagen: Journal of Avian Biology, 31. pp. 527–547.
  5. ↑ Göth, Ann; Booth, David T (22 March 2005). "Temperature-dependent sex ratio in a bird". Biology Letters 1 (1): 31–33. doi:10.1098/rsbl.2004.0247. PMC 1629050. PMID 17148121. Retrieved 1 September 2012.
  6. ↑ Göth, A., & Evans, C. S. (2004). Social responses without early experience: Australian brush-turkey chicks use specific visual cues to aggregate with conspecifics. Journal of Experimental Biology, 207. pp. 2199–2208.
  7. ↑ A case of mistaken identity for Australia’s extinct big bird
  8. ↑ Birks, S. M., and S. V. Edwards (2002). A phylogeny of the megapodes (Aves: Megapodiidae) based on nuclear and mitochondrial DNA sequences. Molecular Phylogenetics and Evolution 23. pp. 408–421.

External links

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