Nest Kept Warm

brown white and black fowl bird stands on top of pike of sticks against a natural forest background

Biological Strategy

Mallee fowl

AskNature Team

Image: Donald Hobern / Flickr / CC BY - Creative Commons Attribution alone

Regulate Reproduction or Growth

Reproduction and growth are two physiological processes that occur in all living systems. There are situations when conditions are right for both, and other situations when continuing either harms the living system because both have a very high energy cost. Reproduction and growth are unique in that both can stop until conditions improve, although stopping either for an extended time can cause problems. An example of regulating reproduction is a process called delayed implantation or embryonic diapause found in some mammals, such as otters. An otter’s embryos sometimes temporarily cease developing and won’t develop further until the female senses that conditions are suitable.

Search this Function

Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

Search this Function

Transform Thermal Energy

Heat is necessary for survival, but too much of it can be damaging to an organism. Explore the ways different living things have adapted to use or transform different types of thermal energy.

Search this Function

Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

Search this Living System

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

Image: Glen Fergus /

Image: Peter Halasz /

Image: Peterdownunder /

“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)