The Nest of the Malleefowl

The malleefowl of southern inland Australia maintains the temperature of its nest within two or three degrees of 34 degrees Celsius (93°F). How can the bird keep this temperature day and night all year long?

Each winter the birds dig a crater about one meter (3 ft) deep by three meters (10 ft) wide, which the male fills with grass, leaves, and other vegetation. After the mound of vegetation is soaked by late winter rains, he digs an egg chamber and covers the whole mound with sandy soil. Soon the vegetation starts to decay and warms, producing a natural incubator.

Diagram of two malleefowls and a cross section of their nest. A. Three eggs in the egg chamber. B. Compost surrounding the egg chamber. C. Layer of insulating soil above the egg chamber. D. The male malleefowl covers the nest by shoveling soil, using his claws while the female malleefowl looks on. — To hatch its eggs **(A),** the malleefowl uses both the warmth of the sun and the heat generated by the composting material **(B).** By adjusting the thickness of the insulating soil **(C),** the malleefowl keeps the eggs at a temperature of about 34 degrees Celsius (93ºF) for many months. To do so, the bird shovels considerable amounts of soil back and forth with its claws **(D)**

Each time the female is ready to lay an egg, the male removes the soil so she can place the egg in the egg chamber. Then he immediately re-covers the mound with soil. She may produce up to 35 eggs between September and February.a

The birds frequently push their bill into the sand and sample it to check the temperature. Then they adjust the mound based on the season. For example:

In the spring when the fermenting vegetation begins to raise the nest temperature too much, the male lets heat escape by scratching away the soil above the egg chamber. Later, he re-covers the nest with the cooled soil.
During the summer, the male puts extra soil on top of the mound to insulate the eggs from the sun. But early each morning, he scratches off the soil, replacing it after the nest and the sand have cooled.
In the autumn when the vegetation has finished fermenting, the male removes almost all of the soil, allowing the midday sun to warm the eggs and the scattered soil. Later, he re-covers the mound with the warmed soil to provide heat during the night.

Each day, on average, the male puts more than five hours of work into transferring about 850 kilograms (1,874 lbs) of soil. The constant movement of the soil has an additional advantage: It keeps the soil loose, which helps the chicks to dig out of the mound when they hatch.

Watch malleefowls scratching soil off of their nest

What do you think? Did the malleefowl’s ability to control the temperature of its nest evolve? Or was it designed?

a The eggs hatch in seven to eight weeks, which prolongs the mound maintenance work into April.