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.
Superprecocial survivors
The incubation period for Nicobar megapode eggs is long, lasting between 70 and 80 days. Females lay between four and five large, pinkish eggs in a clutch, though mounds with up to ten eggs have been observed. The eggs are disproportionately large, weighing up to one-sixth of the adult female's body weight. After laying the eggs, the parents provide no further care.
The chicks are superprecocial, a term describing young that are exceptionally mature and mobile from the moment of birth. After hatching deep within the mound, a chick uses its large, strong feet to dig its way to the surface, a process that can take several days. It emerges fully feathered, with open eyes, and is capable of running and even flying on the same day it hatches. Immediately independent, the young birds can forage for themselves without any parental guidance. This remarkable self-sufficiency results from the unique incubation strategy frees the parents from the demands of brooding and feeding hatchlings.