BIRDS start sitting on their eggs as early as possible to shield them from infection, as well as to warm them to the right temperature.
Ornithologists have long wondered why birds begin to incubate their eggs days before they finish laying a clutch, as this produces a brood of different ages in which the youngest chicks often starve. They had assumed this was to protect the first eggs from temperatures that would interfere with chick development. But Mark Cook, a behavioural ecologist at the University of California, Berkeley, and his colleagues in Puerto Rico found that hen eggs left unprotected…
