The geothermal nest
The Nicobar megapode (Megapodius nicobariensis) is a medium-sized bird endemic to India's Nicobar Islands. It belongs to the Megapodiidae family, a group of birds known as mound-builders. Instead of using body heat for incubation, these birds build large mounds from sand, soil, and decomposing vegetation. The heat generated by microbial decomposition inside the mound is an incubator. Some megapodes also use geothermal heat from volcanic soil or solar-warmed sand.
The male megapode is responsible for mound construction and maintenance. These structures can be massive, with some older, reused mounds reaching over six feet high. The male meticulously regulates the internal temperature, aiming for a stable 33–35°C. Larger mounds, sometimes exceeding 10 cubic meters, are better at maintaining a stable temperature than smaller ones. The bird acts as a living thermometer, using its beak to test the mound's core temperature and then either adding or removing material to make adjustments. This precise temperature control is important, as fluctuations can be lethal to the developing embryos.