Moundbuilders (Megapodiidae)

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Moundbuilders

(Megapodiidae)

Class Aves

Order Galliformes

Suborder Craci

Family Megapodiidae


Thumbnail description
Medium-sized to large chicken-like birds with long legs and toes

Size
11–27 in (28–70 cm); 1.1–5.5 lb (0.5–2.5 kg)

Number of genera, species
7 genera; 22 species

Habitat
Rainforest, subtropical and tropical closed forest, mallee

Conservation status
Endangered: 1 species; Critical: 1 species; Vulnerable: 7 species; Near Threatened: 1 species

Distribution
Islands of Southeast Asia and southeast Pacific, Australia, and Papua New Guinea

Evolution and systematics

The moundbuilders, also known as incubator-birds, brush-turkeys, and megapodes, are chicken-like birds, closely resembling other galliforms such as pheasant and quail in general body shape, plumage, and forest-floor habitat. Their unique method of incubating eggs using environmental heat sources, rather like crocodiles and some reptiles, led some to suggest that these birds were extremely primitive. While this idea has now been thoroughly discredited, there has been considerable discussion about the relationship between the moundbuilders and other galliforms. The most authoritative accounts regard moundbuilders (Megapodiidae) as a sister group of all other galliforms, including the cracids (Cracidae), the South American family they most closely resemble. This classification is followed by the major monograph, The Megapodes, published in 1995.

Although there is a relatively large collection of remains of extinct species from this family, most are from very recent times. They paint a picture of progressive extermination as humans moved through the South Pacific during the last few thousand years. Fossil material from earlier periods is limited, making it difficult to determine the origins of this family. The oldest megapode remains were initially thought to have been found in France, a claim now discredited. This material was used in part to suggest that the earliest moundbuilders had originated in the Northern Hemisphere and subsequently moved south to their present stronghold in the Australasian region. The alternative view is that moundbuilders evolved in the south, probably on the ancient super-continent of Gondwana, and later moved north into Southeast Asia and the Pacific. Although the Southern Origin theory is currently favored, both theories remain speculative due to the lack of reliable fossil material.

Among the Pleistocene remains of moundbuilders are several species much larger than extant species, including Progura gallinacea, from southern Australia, and Megapodius molistructor, from New Caledonia. These and other species, exterminated either directly or indirectly by humans, suggest that as recently as 3,000 years ago, as many as 23–33 additional species of moundbuilders were alive throughout the islands of the South Pacific.

Many of the species exterminated recently belonged to the genus Megapodius, the largest and most widely distributed of all the taxonomic groups within the family. Even excluding these extinct species, the number of species within this genus has puzzled experts for centuries. Harold Frith, the author of this section in the first edition, recognized only four species, which gave a total of 12 species for the entire family. The authors of The Megapodes proposed that there are 22 extant species, which include: 14 species of megapodes, sometimes called the scrubfowl (13 Megapodius and one species in the very similar Eulipoa); three species of brush-turkeys (one Alectura and two Aepypodius); three species of talegallas (Talegalla); and two species belonging to single-species genera, the malleefowl (Leipoa) and the maleo (Macrocephalon).

Physical characteristics

Moundbuilders have large, strong legs and feet and a short down-curved bill. Generally, most moundbuilders resemble other galliforms in body shape and drab plumage. In those few species in which the plumage is patterned or colorful, the effect is one of camouflage rather than conspicuousness. Most species are mainly drab brown, gray or blackish in color without detailed patterning, the main exception being the malleefowl (Leipoa ocellata). In this species the plumage is heavily spotted, with the patterns resembling eye shapes (ocellated). The most distinctive plumage of any moundbuilder is that of the maleo (Macrocephalon maleo) from Indonesia, a relatively large species whose dark blackish upperparts and head starkly contrast with its elegant salmon breast.

Although most moundbuilders have fairly drab plumage, many have naked patches of red, yellow, or blue skin on the face and neck, though this is rather inconspicuous. The three species of brush-turkey, however, each possess brightly colored skin on a virtually naked neck and head. The males in these species also possess a variety of sometimes oddly shaped wattles, combs, and neck sacs. These ornaments, vividly colored in yellows, reds, and blues, are used in sexual and dominance displays. In species such as the Australian brush-turkey (Alectura lathami), the large bright-yellow neck sac develops only among breeding adult males and is used as a signal of status. It may also be inflated for use as a device for enhanced vocalization.

Distribution

Moundbuilders are found mainly in Australia and New Guinea and on a large number of islands throughout the southeastern Pacific and Southeast Asia. They extend from the remote island of Niuafo'ou, Tonga, in the west, to the Palau and Mariana islands in the north, and Nicobar and Andaman islands in the Bay of Bengal to the east. Within this region, they occur west of Wallace's Line (between Borneo and Sulwesi) and are, therefore, largely an Australasian rather than an Oriental group. This is supported by the absence of moundbuilders from most of the larger land masses of the region, including most of Borneo, Java, Sumatra, and the mainland of Southeast Asia.

This largely island-based distribution has been explained as resulting either from competition for food with other galliforms present in the area (mainly pheasant and jungle fowl), or from predation pressure from carnivores, primarily civets and civet cats. The latter hypothesis suggests that these predators have prevented the expansion of moundbuilders onto the larger landmasses for reasons directly related to their methods of incubation; the use of incubation mounds requires attendance for prolonged periods of time, a situation making them vulnerable to predators. In the small number of locations in which feline predators and moundbuilders occur together, the birds involved do not build mounds but are burrow-nesters, laying in soil heated by the sun or volcanic activity.

Habitat

Moundbuilders are largely birds of tropical and subtropical rainforests. Although some species venture into more open habitats and certain locations with seasonally dry climates, the moundbuilding habits of most require conditions that enhance the decomposition of organic matter. Even the burrow-nesting species, which may travel to exposed beaches or geothermal areas for egg-laying, typically return promptly to forests when finished.

Only two species are routinely found in habitats other than dense, moist forests. The malleefowl is the most aberrant of all species in this regard, living in the dry scrub of dwarf eucalyptus trees, or mallee, of south Australia. The only other species found in drier habitats are relict populations of the Australian brush-turkey. In general, this bird is an edge-species, preferring the margins of rainforests for its mounds, but some populations occur in the dry scrub forests far inland.

Behavior

Almost every aspect of life among moundbuilders is influenced by their incubation methods. Because eggs are laid in individual holes deep within the incubation site, each chick hatches separately, and, without assistance from parents, digs for 2–15 hours to reach the surface. Adult moundbuilders appear not to recognize the young of their own species. All hatchlings must, therefore, be able to leave the incubation site, find food and water, recognize and avoid predators and, even thermoregulate, alone. Malleefowl chicks (Leipoa ocellata) can run swiftly within one hour and fly within 24 hours of their hatching. Chicks of moundbuilders are certainly among the most precocial of all birds, and some experts now define their behavior as "supercocial"—meaning the young are completely independent at hatching. Studies of juvenile Australian brush-turkeys by Ann Göth have confirmed that, despite the absence of assistance by adults, these birds are able to respond differently and appropriately to aerial versus ground predators

The incubation sites used by these birds, both mounds and burrows, are the only sites in which eggs can be laid. In most species, construction and maintenance of these sites is undertaken jointly by a mated male and female. In these pairings, members are rarely seen separately and appear to be monogamous. However, detailed investigations of the Nicobar megapode (Megapodius nicobariensis) revealed examples of mate-exchanges and extra-pair copulations, and at least one

case of polygyny has been recorded in the otherwise monogamous malleefowl.

In the three species of brush-turkeys, monogamy clearly does not occur. Males construct large incubation mounds alone and defend these from other males. Males allow access only to females willing to mate with them. In Australian brush-turkeys, males may construct several mounds or may take over another male's mound nearby. Females have unrestricted choice among all the mound-defending males, although there may be considerable competition for particular mounds among them. Although it is unclear how females choose among males, some individual males attract a large proportion of the eggs while other males attract very few.

All moundbuilders produce a variety of typical galliform-like clucks, grunts, and squawks, all of a low frequency, deep in pitch and generally fairly low in volume. Two species produce a distinctive, low-frequency boom by inflating either the external neck sac (Australian brush-turkey) or chambers in the throat (malleefowl) and then forcing air out through the nostrils. Many species—all Megapodius as well as the maleo—also produce a series of remarkably loud and conspicuous calls during both the day and night. Male brush-turkeys communicate with booms to advertise their mounds to females or to assert themselves while engaged in aggressive male-to-male behavior. In some places, the effect of roosting groups of these birds answering one another in these very loud and raucous choruses for prolonged periods, can be a memorable, if sleep-disturbing, experience of being in the tropical jungle.

Feeding ecology and diet

Most moundbuilders appear to be generalist forest-floor foragers, eating a very wide variety of food types but taking advantage of seasonal abundances of items such as fallen fruits. Although the few studies on feeding ecology mention large amounts of small leaf-litter invertebrates along with fruit and seeds being eaten, unusual items such as ants, scorpions, and even small snakes are also mentioned.

While most of these items will be encountered as the birds rake their way through the leaf-litter, moundbuilders also seek out specific types of food. For example, Australian brush-turkeys excavate large holes in the forest floor in order to gain access to the succulent tubers of certain rainforest plants. This species also feeds on fruit within the forest canopy.

Reproductive biology

While many of these birds may look like large and somewhat dull galliforms, it is their unique approach to incubation that sets the moundbuilders apart from all other birds. The discovery of their unusual incubation sites was discussed by Bernard Grzimek himself in the first edition of this work. It was Navarette, a monk on Magellan's ill-fated circumnavigation of

the world (1519–1522), who gave us the first European account of a moundbuilder, probably the Philippine megapode (Megapodius cumingii). Unfortunately, Navarette's less-than-precise description did not aid the scientific reception of these ideas; in Grzimek's words, "[the monk] brought back… the story of fowl which laid eggs larger than themselves in heaps of leaves. The eggs, then, hatched without any further care. The matter of the size of the eggs was not quite correct; in regard to the second point, people believed more in mermaids and giant sea serpents than in such skills in fowl."

It is now known that this family of birds exploits three different sources of natural heat: solar radiation (primarily on beaches), geothermal activity (especially the soil near volcanic areas), and the decomposition of organic matter (in mounds). In the third process, decomposition, heat results from the respiration of the microorganisms that break down the material gathered together into a mound. Most species construct some form of incubation mound and this is the activity that gives the family its common name.

Incubation mounds vary greatly in size and composition but all consist of moist organic matter, mainly leaf-litter and soil, in which microbes can proliferate. The birds maintain a reliable incubator for many months by carefully and regularly adding fresh material to conserve moisture and prevent drying. The male brush-turkey and malleefowl maintain the temperature of the mounds at 91°F (33°C) by opening the mounds to cool them or piling on more sand. They probe the mounds with their bills to check the temperature. The amount of work required to construct and maintain a mound varies greatly among species and with climatic conditions. By far the most complex mounds are those made by malleefowl. Living in arid areas, this species faces the challenge of gathering together large amounts of damp leaf-litter and preventing the material from drying out. It does so by excavating a shallow depression, filling this with plant material, and waiting for rain. This debris is then piled into a mound and buried beneath a huge layer of sand and dry soil, which effectively insulates the mound. Whenever the birds need to gain access to the inner egg chamber for egg laying or temperature testing, they must remove and replace up to 1,875 lb (850 kg) of sand.

The incubation mounds of most other moundbuilders require much less effort to construct and maintain, many being little more than a large pile of leaf-litter, or simply a gathering of material around the base of a rotting log. Such mounds are made annually and often decompose to a small soil hump. Species such as the orange-footed megapode (Megapodius reinwardt), however, use the same mound year after year, with the resulting construction often growing to hillocks 14.8 ft (4.5m) in height and more than 29.5 ft (9 m) in diameter.

Some species, including certain populations of those constructing mounds, are actually burrow-nesters rather than mound-builders, incubating their eggs in material that is heated by the sun or geothermal sources. In most cases, the eggs are laid in the loose soil at the bottom of long burrows excavated into the substrate.

Moundbuilders lay their eggs at intervals of several days, unlike most birds that lay eggs at smaller intervals. Each egg begins to develop immediately upon being deposited in the warm material. A female may lay a total of 12–30 very large (2.6–8.1 oz [75–230 g]) eggs per season, an egg mass that may comprise 120–180% of her body weight. Moundbuilder eggs contain an extremely high (32–49%) proportion of weight as yolk, a feature than correlates with their prolonged incubation period of 45–70 days.

Conservation status

Of the 22 extant species of moundbuilders, almost half face some level of threat. The Polynesian megapode (Megapodius pritchardii), which is limited to a single tiny island and may number less than 300 individuals, is Critically Endangered; and the Micronesian megapode (Megapodius laperouse), which is threatened by a variety of natural and human-based disturbances, is Endangered. A further seven species are classified as Vulnerable, due mainly to habitat loss, over-exploitation of eggs by humans, and predation by introduced animals such as foxes.

Significance to humans

The moundbuilders have had a close relationship with indigenous peoples for millennia throughout their range. Wherever they occur, humans have harvested their eggs, an extremely important source of protein and portable food. While humans have undoubtedly been responsible for the disappearance of numerous species, especially in the South Pacific, in other places, the exploitation of megapode eggs seems to have been practiced carefully for thousands of years. More recently, however, sustainable harvesting appears to have broken down through human population growth and internal migration. Today the conservation of several threatened species is being undertaken by indigenous programs that aim to restore habitat and prevent over-harvesting.

Species accounts

List of Species

Australian brush-turkey
Malleefowl
Maleo

Australian brush-turkey

Alectura lathami

taxonomy

Alectura lathami Gray, 1831, Sydney, Australia. Two subspecies recognized.

other common names

English: Scrub turkey, bush turkey, pouched talegallus; French: Talégalle de Latham; German: Bruschhuhn; Spanish: Talégalo Cabecirrojo.

physical characteristics

23.6–27.6 in (60–70 cm); female 4.4–5.5 lb (1.98–2.51 kg), male 4.6–6.4 lb (2.12–2.9 kg). Large, mainly black, ground-dwelling bird with bright red head and neck, males with either yellow or light purple extendable neck sac during breeding season. Chicks, born fully feathered, have a uniform color buff-brown to sooty brown, closely resembling quail.

distribution

East Australia, from Cape York to northern New South Wales.

habitat

Rainforest and closed forest.

behavior

Loosely social, males building and defending incubation mounds. Roosts communally in trees.

feeding ecology and diet

Generalist ground-forager, feeding on leaf-litter invertebrates and fruits.

reproductive biology

Mounds constructed in July and are maintained until about December. Males polygynous, maintaining mounds (often two) in which females lay several eggs before moving to another mound. Up to 18–24 eggs; white and elliptical; laid by each female although a mound may have incubated up to 50 by the end of the season. Young extremely precocial.

conservation status

Abundant and locally common throughout most of range, especially in southern Queensland where it is often a nuisance in urban gardens.

significance to humans

Eggs harvested.


Malleefowl

Leipoa ocellata

taxonomy

Leipoa ocellata Gould, 1840, Swan River, Western Australia. Monotypic.

other common names

French: Léipoa ocellé; German: Thermometerhuhn; Spanish: Talégalo Leipoa.

physical characteristics

23.6 in (60 cm); female 3.3–4.5 lb (1.52–2.05 kg), male 4.0–5.5 lb (1.81–2.50 kg). Large and distinctive, upper parts boldly

barred, streaked and fringed with gray, white, black, and rufous. Sexes similar though males slightly larger.

distribution

Originally found widely throughout the inland of southern Australia, now restricted to small patches of suitable habitat in southern states of Australia. Recently desert populations rediscovered in central Australia.

habitat

Arid and semi-arid low eucalypt and acacia woodland (mallee) and heath.

behavior

Territorial, pairs defending area of incubation mound. Often solitary, with male spending long periods near mound while female wanders widely. Roost in trees and rarely fly. Three main calls: three-syllable booming (territorial), loft lowing call (communication), and sharp grunt (alarm).

feeding ecology and diet

Very broad diet of largely plant materials, especially seeds, fruit, and buds although up to 20% of food taken is ground-dwelling invertebrates.

reproductive biology

Breed at two to four years of age. Mound-building species, with male spending up to 11 months of each year in mound construction and attendance. Mounds may be used for several generations. Usually strictly monogamous though some cases of polygyny are known. Females lay 2–34 eggs at intervals of 5–10 days. Each egg weighs 10% of female's body weight, the egg's pale pink color changes to dark beige during incubation. Incubation takes 55–77 days, depending on temperature of mound.

conservation status

Classified by IUCN as Vulnerable, species having undergone 20% decline during last 45 years due to habitat destruction and impact of introduced predators.

significance to humans

Species has strong totemic significance for Central Australia indigenous people.


Maleo

Macrocephalon maleo

taxonomy

Macrocephalon maleo S. Müller, 1846, Sulawesi. Monotypic.

other common names

English: Gray's brush-turkey, maleofowl; French: Mégapode maléo; German: Hammerhuhn; Spanish: Talégalo Maleo.

physical characteristics

21.7 in (55 cm); females 3.3–3.9 lb (1.50–1.76 kg), males 2.9–3.5 lb (1.34–1.59 kg). Large, striking bird with upperparts deep black and underparts white with strong salmon-pink tinge. Head topped with distinctive black casque. Sexes very similar, though males slightly larger.

distribution

Endemic to island of Sulawesi, Indonesia, though absent from all deforested areas.

habitat

Tropical forests, as well as secondary vegetation and plantations.

behavior

Shy and wary when approached. Pairs inseparable and will drive other pairs away from favored egg-laying positions.

feeding ecology and diet

Omnivorous, feeds on wide variety of fruits, seeds, and invertebrates encountered while foraging on forest floor.

reproductive biology

A burrow-nesting species, using geothermally heated soils in the forest or sun-exposed beaches. Pairs travel to nesting grounds together and share effort in excavating laying hole and chasing away other maleos. Eggs laid at depths of 4–40 in (10–100 cm), at intervals of 10–12 days, the longest interval of any bird.

conservation status

Classified as Vulnerable by the IUCN due to rapid population decline and over-exploitation and habitat degradation.

significance to humans

This charismatic species is an important species to the people of Sulawesi, where its eggs have been harvested for centuries.


Resources

Books

Bird, David M. The Bird Almanac: The Ultimate Guide to Essential Facts and Figures of the World's Birds. Buffalo: Firefly Books, 1999.

Dekker, R., R. Fuller, and G. Baker. Megapodes: Status Survey and Conservation Action Plan 2000–2004. Cambridge, United Kingdom: IUCN, 2000.

Harrison, Colin, and A. Greensmith. Birds of the World. New York: Dorling Kindersley Inc., 1993.

Jones, D., R. Dekker, and C. Roselaar. The Megapodes. Oxford: Oxford University Press, 1995.

Whitfield, P., ed. The MacMillan Illustrated Encyclopedia of Birds. New York: Collier Books, 1988.

Periodicals

Göth, A. "Innate Predator-recognition in Australian Brush-turkey (Alectura lathami, Megapodiidae) Hatchlings." Behaviour 138 (2001): 117–136.

Organizations

WPA/BirdLife/SSC Megapode Specialist Group. c/o Department of Ornithology, National Museum of Natural History, P.O. Box 9517, Leiden, 2300 RA The Netherlands.

Other

Malleefowl Conservation Group, Inc., 25 Nov. 2001. 9 Dec. 2001. <http://www.malleefowl.com.au>

Wong, Sharon. "Development and Behaviour of the Australian Brush-turkey Alectura lathami," Griffith University, 1999. Australian Digital Theses Project. 9 Dec. 2001. <http://www.gu.edu.au/ins/lils/adt/approved/adt>

Darryl Noel Jones, PhD