Moundbuilders

The megapodes, or moundbuilders, are a fascinating group of birds found in Australia, New Guinea and its surrounding islands, eastern Indonesia, and the Philippines. Also known as “thermometer birds,” scrubfowl, or brush turkeys, 22 species are recognized (seven genera) in the family Megapodiidae. A wide range of habitats are occupied by these species, ranging from semiarid scrublands of Australia to tropical rainforests of Indonesia.

Megapodes are largely ground-dwelling birds, but many seek refuge in low branches if alarmed or threatened by predators. Most species feed on a wide range of insects, worms, snails, seeds and berries. With few exceptions, megapodes are dull colored birds: the plumage is generally dark brown and black or gray in appearance. All are about 20 inches (50 cm) in total length, with large rounded wings and a medium-long tail. The legs and feet are sturdy, while the head is small. The head and neck of brush turkeys are bare apart from several coarse hairs.

One of the most unusual features of these birds is their habit of not incubating their eggs directly. Instead, they have devised a range of ingenious techniques which enables them to be free of the hazardous task of sitting on a clutch of eggs for several weeks at a time. All species of megapodes have evolved different means of overcoming this burden, but they all rely on the use of natural resources to heat and incubate their eggs. The scrubfowl (Megacephalon ) display one of the simplest techniques: a nest site is carefully chosen and dug on a beach, often black volcanic ash or sandy soil exposed to the sun, where the female lays up to 30 eggs. When covered, the heat of the sand is sufficient to incubate the eggs and the parent birds have no further responsibility at the nest site.

When the chicks hatch, they dig their own way out of the nest and quickly seek shelter in surrounding vegetation. Most can fly within 24 hours of emerging from the nest. Another simple manner of laying a clutch is seen in M. freycinet, which lives on islands off the Queensland coast in Australia and lays its eggs in simple cracks in exposed rocks, the sun’s radiation being enough to incubate the eggs.

A far more complex ritual is practiced by forest-dwelling megapodes, which may construct large mounds (measuring up to 33 feet [10 m] in diameter and 16 feet [5 m] in height) of earth and vegetable material. Several pairs of birds may cooperate in the construction of such large incubating chambers. Once the mound has been constructed the male birds carefully monitor the inside temperature by probing the mound with their beaks. In addition to any solar radiation, as the vegetation decomposes in the warm, moist environment of the forest, it gives off heat, thereby providing ideal conditions for incubation. If the temperature is too high, the male removes some of the material and mixes the contents to allow air to circulate; similarly if it is too cool, additional materials may be added to the pile. The ideal temperature is thought to be in the region of 90–95°F (32–35°C). Only when the males are satisfied that the mound has reached a correct and stable temperature will the females begin to lay. Once they have done so, the males continue to monitor the daily temperature, until such time as the chicks emerge.

Megapodes and humans have always had a close relationship: although some adult birds are killed for food, it is their eggs that are the real treasure and these have been collected for food throughout history. While some species lay individual clutches of up to 30 eggs, others lay communally and often in very large numbers, particularly the maleo (Macrocephalon maleo ), Moluccan megapode (Eulipoa wallacei ), Polynesian megapode (Megapodius pritchardii ) and the Melanesian megapode (Megapodius eremita ).

At some of these sites, tens of thousands of eggs may be laid each year. These offer ideal facilities for villagers to collect the eggs for food or trade purposes. While this exploitation was once carried out in a sustainable manner—many villages set strict quotas on the number of eggs that could be taken from individual mounds at a time—such practices have now largely disappeared. Continuing collection, as well as habitat loss and degradation from logging operations and agriculture which degrade the bird’s habitat have, in many cases, now reduced local populations to the point that the harvest is no longer sustainable.

While human offtake and habitat loss have certainly played a major role in the demise of many species, many megapodes have also suffered as a result of ground predation. All of these species evolved in regions where the threat of ground predators was absent or very low. In recent decades, however, many species have been introduced by humans, particularly cats, dogs, rats and foxes, which have had a disastrous effect on many megapode populations. Introduction of feral predators is known to have decimated several populations in many Polynesian islands, leading to local extinctions. Other species, such as the Polynesian megapode on Niuafo’ou Island and the Tonga are also threatened by natural events, such as potential volcanic eruptions.

See also Extinction; Predator.