Megapode

Description

Megapodes are medium-sized to large terrestrial birds with large legs and feet with sharp claws, which assist them in the preparation of pits and mounds to incubate their eggs. Megapodes are of three kinds: scrubfowl, brush turkeys, and mallee fowl or lowan. 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.

Distribution and habitat

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. Raoul Island, a New Zealand territory and the main island of the Kermadec Islands, may also have once had a species of megapode, based on settler accounts.

Behaviour and ecology

Megapodes are mainly solitary birds that do not incubate their eggs with their body heat as other birds do, but bury them. In this their behaviour resembles that of turtles and crocodiles more closely than that of other birds. Their eggs are unusual in having a large yolk, making up 50–70% of the egg weight. There are three methods of incubation. Most of the family (about 13 species) are best known for building massive nest mounds of decaying vegetation, which generate heat through microbial decomposition, and to which the male attends, adding or removing litter to regulate the internal heat while the eggs develop. However, some (3 species) 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 the sand. Some (6 species) use a combination of incubation strategies depending on the local environment.

Although the Australian brushturkey was thought to exhibit temperature-dependent sex determination, this was later proven false; temperature does, however, affect embryo mortality and resulting offspring sex ratios. The nonsocial 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. Research suggests an instinctive visual recognition of specific movement patterns is made by the individual species of megapode.

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. In megapodes superprecociality apparently evolved secondarily from brooding and at least loose parental care as more typical in Galliformes. Eggs previously assigned to Genyornis have been reassigned to giant megapode species. Some dietary and chronological data previously assigned to dromornithids may instead be assigned to the giant megapodes.

Megapodes share some similarities to the extinct enantiornithes in terms of their superprecocial life cycle, though also several differences.

Species

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

Phylogeny

Taxonomy

• Genus †Mwalau Worthy et al. 2015
  • †Mwalau walterlinii Worthy et al. 2015 (Vanuatu)
• Genus †Ngawupodius Boles & Ivison 1999
  • †Ngawupodius minya Boles & Ivison 1999
• Scrubfowl group
  • Genus: Macrocephalon
    • Maleo, Macrocephalon maleo
  • Genus: Eulipoa (sometimes included in Megapodius)
    • Moluccan megapode, Eulipoa wallacei.
  • Genus: Megapodius
    • Tongan megapode, Megapodius pritchardii
    • Micronesian megapode, Megapodius laperouse
      • Marianas Island megapode, Megapodius laperouse laperouse
      • Palau Island megapode, Megapodius laperouse senex
    • Nicobar megapode, Megapodius nicobariensis
    • Philippine megapode, Megapodius cumingii
    • Sula megapode, Megapodius bernsteinii
    • Tanimbar megapode, Megapodius tenimberensis
    • Dusky megapode, Megapodius freycinet
      • Forsten's megapode, Megapodius (freycinet) forstenii
    • Biak scrubfowl, Megapodius geelvinkianus
    • Melanesian megapode, Megapodius eremita
    • Vanuatu megapode, Megapodius layardi
    • New Guinea scrubfowl, Megapodius decollatus
    • Orange-footed scrubfowl, Megapodius reinwardt
    • †Pile-builder scrubfowl, Megapodius molistructor Balouet & Olson 1989
    • †Viti Levu scrubfowl, Megapodius amissus Worthy 2000
    • †Consumed scrubfowl, Megapodius alimentum Steatman 1989a
    • †M. andamanensis Walter 1980 nomen dubium [oospecies]
    • †M. burnabyi Gray 1861 nomen dubium [oospecies]
    • †Raoul Island scrubfowl, M. sp.
    • †'Eua scrubfowl (small-footed megapode), M. sp.
    • †Lifuka scrubfowl, M. sp.
    • †Stout Tongan megapode, M. sp.
    • †Large Solomon Islands megapode, M. sp.
    • †New Caledonia megapode, M. sp.
    • †Loyalty megapode, M. sp.
    • †New Ireland scrubfowl (large Bismarck's megapode), M. sp.
• Malleefowl, group
  • Genus: Leipoa
    • Malleefowl, Leipoa ocellata
• Brushturkey group
  • Genus: Alectura
    • Australian brushturkey, Alectura lathami
  • Genus: Aepypodius
    • Wattled brushturkey, Aepypodius arfakianus
    • Waigeo brushturkey, Aepypodius bruijnii
  • Genus: Talegalla
    • Red-billed brushturkey, Talegalla cuvieri
    • Black-billed brushturkey, Talegalla fuscirostris
    • Collared brushturkey, Talegalla jobiensis
  • Genus: †Progura
    • Progura gallinacea – Queensland, Pleistocene
    • Progura campestris – South Australia, Pleistocene
  • Genus: †Latagallina
    • Latagallina naracoortensis formerly Progura naracoortensis – New South Wales, South Australia, Pleistocene
    • Latagallina olsoni – South Australia, Pleistocene
• Incertae sedis
  • Genus: †Garrdimalga
    • Garrdimalga mcnamarai – South Australia, Pleistocene

Human uses

The particular requirement of some species of megapode who incubate their eggs in soil heated by volcanoes, has led to the creation of relatively small nesting areas which need to accommodate thousands of birds. The massive seasonal accumulation of eggs in these areas, and their high yolk to white ratio, has resulted in them becoming a major source of food for humans.

In their native Oceania, indigenous peoples protect their nesting sites, as their eggs are considered to be delicacies. Their eggs are about twice the size of chicken eggs and the yolks are roughly four times as massive. Among the peoples who live near megapode habitats, megapode eggs are regularly gifted as signs of loyalty, friendship and respect.

The context of egg harvesting by humans has undergone recent cultural changes. While it was formerly regulated by ritual conventions which restricted the harvest to particular castes and the consumption to local communities, since the 1950's the limitations have disintegrated. The egg harvest reached its peak in the 1970's, when it was estimated that between 4-8.9 million Melanesian megapode eggs were harvested annually, in Pokili alone. As of 2000, out of the 131 original nesting sites, 42 were abandoned, 38 were severely threatened, 34 were threatened, 12 were of unknown status and only 5 were considered viable. Nine megapode species are considered at risk of extinction.