The nests of mallee fowl provide warmth for eggs by use of rotting vegetation.

“One family of birds has, in the most ingenious way, managed to avoid the hazardous duty of sitting on its eggs throughout the incubation period. The mallee fowl of eastern Australia lays its eggs in a large mound built by the male. The core is composed of rotting vegetation and the whole is covered with sand. The breeding season is a very long one, spread over five months, and during all this time, the male has to remain in constant attendance probing the mound with his bill to test the temperature. In spring the newly gathered vegetation at the centre is decaying rapidly and producing so much heat that the mound may get too warm for the eggs within it, in which case he industriously removes sand from the top to allow heat to escape. In summer, there is a different danger: the sun may strike the mound and over-heat it. Now he must pile more sand on top as a shield. In autumn, when the decaying core has lost much of its strength, he removes the top layers to allow the sun to warm the centre where the eggs are and then covers it in the evening to retain the heat.” (Attenborough 1979:196-197)

“Scrub fowl attack the daily supervision and reconstruction of their mounds as if the laws of heat distribution were entirely in their grasp. It seems as if, after establishing the interior temperature, they need only choose the proper profile of the breeding plant to maintain that temperature. The mallee fowl considers the existing climatic conditions instinctively (and, it seems, very sensibly) while it proceeds with its regulating activity. In spring, temporary air shafts are used to siphon off superfluous fermentation heat. When fermentation abates in summer and irradiation from the sun increases, the birds prevent overheating by piling up more sand and adding considerably to the height of the mound; they rely on inertia in the warming up of a large mass. Should nevertheless the heat of the sun penetrate dangerously deep, they change their tactics. They dig the breeding mound early in the morning and spread the sand for cooling. When it has cooled off, it is again used to build the pile up…Finally, when both fermentation and irradiation from the sun abate in the fall, the bird operates with a very thin layer of sand only, which quickly warms up in the sun. At the same time, sand is being heated in the sun close to the breeding mound under constant stirring; it is then mixed warm into the pile.” (Tributsch 1984:137)

Last Updated September 14, 2016