by Nancy Trautmann
In Australia, there is a bird called the Brush-turkey (Alectura lathami) that builds compost piles to incubate the eggs so that they won't have to sit on them! They build mounds of decomposing vegetation, and the heat produced by the microbial decay maintains the eggs at about 33°C (92°F), 15°C warmer than the ambient air temperature. Because each nest generates more than 20 times the heat production of a resting adult Brush-turkey, many more eggs can be incubated this way than if they relied on warmth from the parent birds. Initially the adult birds tend the composting nest, occasionally mixing and either adding or removing vegetation as needed to regulate the temperature, which they sense through their bills. After this initial adjustment, the nests require little attention, and larger ones can stay warm for several weeks without tending.
The largest nests are on Kangaroo Island in South Australia, where the average mound measures about 12.7 cubic meters and weighs about 6,800 kg. Scientists have constructed a computer model using data on mound size, ambient temperature, and the nest's rate of heat production, water content, dry density, and thermal conductivity. The model predicts that as little as 1 cm of litter added to the mound will raise the core temperature about 1.5°C. Experiments indicate that the composting nests require (1) a critical mass of fresh litter (ca. 3,000 kg), (2) sufficient water content (> 0.2 ml/g dry material), and (3) occasional mixing of the litter.
For more information on this clever bird, see this article:
Seymour, R.S. and D.F. Bradford. 1992. Temperature regulation in the incubation mounds of the australian Brush-turkey. Condor 94(1): 134-150.
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