There are some animals you look at and wonder: How in the world did they evolve? One such bird is the megapode. This is a bird that, to carry on its species, creates a nest that incorporates materials science, biochemistry, physics, and heavy construction work.
How did this unusual-looking bird invent a self-heating building, thousands of years before we humans did? It's one of the mysteries of nature.
Top image: Michael Jefferies/Flickr.com
If you are wandering around the forests of the Pacific Islands, Southeast Asia, or the countryside in Australia, you may chance upon a mound that looks like the kind of thing people would dump out while they were excavating for a swimming pool. You'd glance around nervously, wondering who else was out there, and if you were lucky you'd see what looked like a small black turkey. That turkey will already be angry at you for disturbing its nest, but if it could hear what you were thinking it would also be angry with you for underestimating its engineering prowess. This animal built the kind of self-heating building that humans wouldn't be able to manage for millenia.
The megapode, for that is what you have just chanced upon, starts out its nesting process by digging a good ways into the ground — up to about a yard deep. Then it starts collecting leaf litter, filling the hole and building, building, until it creates a mound that's around ten to twelve feet in diameter. On top of this they layer sand, and above that they have another layer of leaf litter. Between the leaf litter and the sand, they deposit their eggs. They then tend to the nest for the rest of the incubation period.
And it is, quite literally, an incubation period. Most people, when walking through deep dead underbrush or jumping into a mound of raked leaves, will notice that it's slightly warm inside. As bacteria break down organic matter, they heat produce carbon dioxide, water, and heat. By building a giant mound full of nothing but packed dead leaves and twigs, the megapode has managed to make a heater that will keep its eggs warm while it goes about its business. Its business has to be constantly interrupted, though, because decomposition goes through many stages. One stage produces a small amount of heat, and later stages cranks the heating up. The megapode has managed to measure what stage the material of the nest is in, and adjusts its size and composition accordingly throughout the incubation of the eggs.
This creates two different puzzles for biologists. The first puzzle is how megapodes evolved to manage the thermodynamics of their decomposing leaf litter. It's hard enough to keep eggs at a constant temperature under the best of conditions. This bird is managing both the biochemistry and physics of a structure much larger than itself, for weeks at a time.
The other, and stranger, puzzle revolves around how megapodes manage to recognize each other. The layer of sand at the top of the mound insulates the nest and keeps predators out. It also would keep helpless baby birds in. Baby megapodes, however, are not helpless. They are superprecocial, and claw their way out of the giant nest fully able to run, hunt, and fly on the very first day. They then scatter and live alone, skipping even the slightest bit of imprinting.
This fact causes biologists to wonder how the birds even manage to recognize other birds of the same species enough to mate, and create the necessity for nests in the first place. Some researchers speculate that the birds have an instinctive way of recognizing movements or scents that are enough like their own, but it seems these creature's entire lives are simply pre-programmed into their heads — with no examples, no instructions and no blue prints. When going on instinct means building structures so large that a human family could shelter in them for the night, it starts to look like the forces of evolution are just having sport with us.
Second Image: Peter Halasz