Further Observations on the Black-breasted Buzzard Hamirostra melanosternon Using Stones to Break Eggs

Abstract

A naive, captive juvenile Black-breasted Buzzard Hamirostra melanostemon, hand-reared in isolation, used stones to break large eggs and feed on the contents. In a series of trials conducted over two days, it was provided with c. 15 stones (10-80 g in weight) and whole eggs of domestic goose Anser anser, Rhea Rhea americana and domestic turkey Meleagris gallopavo. It threw the stones from its raised bill, from a standing position on the ground, and favoured rounded stones in the intermediate (40-60 g) size range. The bird became more proficient with practice, requiring fewer blows to open an egg as the trials progressed. It is concluded that stone-throwing is innate behaviour, modified by experience.