• Consider the Evidence from the Animal World
    Awake!—1978 | April 8

    • A Marvel of Heat Regulation

      The Mallee fowl of Australia accomplishes a feat that humans would find practically impossible without the use of modern sophisticated devices​—he makes his own incubator.

      In the dry semidesert that is his home, where temperatures range from 17 degrees Fahrenheit (−8 degrees Celsius) to 115 degrees Fahrenheit (46 degrees Celsius), the male Mallee fowl buries leaves during the winter while they are still moist so that they will not dry out but will decay. In May, with the approach of winter, he digs a hole 15 feet (4.6 meters) in diameter and 3 to 4 feet (1 to 1.2 meters) deep, raking in the leaf litter from as far as 40 yards (36.5 meters) around. Then, in the cold of August, he covers the heap with soil up to two feet (.6 meter) thick. The female then lays eggs in a hole in the top of the mound.c

      A researcher on this matter, H. J. Frith, as reported in Scientific American, August 1959, pp. 54-58, says:

      “In the spring [the male Mallee] must reduce the amount of fermentation heat reaching the eggs. He visits the mound before dawn each day and digs rapidly until he nears the egg chamber. After allowing just enough heat to escape he refills the hole with cool sand.

      “Later in the summer the sun gets very hot, and much heat moves by conduction from the surface of the mound to the egg chamber. Some heat still moves up also from the organic matter, though fermentation is slowing by this time. The eggs thus tend to overheat, and the bird must do something to reduce the temperature. There is little he can do to slow the fermentation rate, but he does lower the rate of solar conduction. Daily he adds more soil to the mound. As the mound grows higher and higher, the eggs for a while are more thoroughly insulated from the sun. After a time, apparently, the bird can build the mound no higher, and a wave of heat begins to go down toward the eggs again. Now the male bird visits the mound each week or so in the early morning, removes all the soil and scatters it in the cool morning air. When it is cool, he collects it and restores it to the mound. This is strenuous work, but effective in destroying the heat wave in the incubator. The temperature in the egg chamber remains steady at 92 degrees [33 degrees Celsius].

      “When autumn comes, the bird is faced with the opposite problem: falling temperature in the mound. The mound no longer generates fermentation heat, and the daily input of solar heat is declining. The bird now changes his activities to meet the challenge. Whereas he had scratched and scattered the sand to cool it in the early morning, often before dawn, he now comes to the mound each day at about 10 a.m., when the sun is shining on it. He digs almost all the soil away and spreads it out so that the mound resembles a large saucer, with the eggs only a few inches below the surface. This thin layer of soil, exposed to the midday sun, absorbs some heat, but not enough to maintain the temperature throughout the night. The saucer must be refilled with heated sand. Throughout the hottest part of the day the bird scratches over the sand he has removed from the mound, exposing all of it to the sun. As each layer gets hot, he returns it to the mound. He times the work so that the incubator is restored with layers of heated sand by 4 p.m., when the sun is getting low.”

      This researcher experimented by placing a heating element, operated by a 240-volt generator, in the mound, switching the heat on and off. This kept the male bird busy, but he managed to maintain the temperature at nearly 92 degrees.

      What power of blind chance would let this bird know that a temperature of 92 degrees Fahrenheit (33 degrees Celsius) was absolutely essential to the incubation of the eggs, and, for that matter, why would this bird want to bring forth offspring at all? In the Mallee fowl’s case it is more a matter of wonder, for when the young bird hatches and digs out of the mound, the parent birds leave it absolutely on its own. They give it no help at all. Yet the male bird has done some of the heaviest work under a blazing sun in order to incubate the eggs, as though the continuation of the Mallee bird species was important to the ecology, which it no doubt is.