Family values

摘要

The private life of the Verreaux's (or black) eagle, a spectacular raptor of the drier parts of Africa, does not exactly embody Victorian family values. The female nearly always lays two eggs, a few days apart, which hatch into two chicks, one a little bigger than the other. As soon as the smaller hatches it is turned upon by its sibling, which attacks it viciously, the assault almost invariably leading to death. In one nest that was continuously watched by the ornithologist Valerie Gargett, the bigger chick pecked its nest-mate 1,569 times in its brief 72-hour existence. Throughout this period, the parents did nothing to intervene. Ornithologists used to call this phenomenon 'cainism' but today use the less poetic, but less sexist, term 'siblicide'. Obligate siblicide occurs in some other raptors as well, and in species of boobies, penguins, egrets and pelicans. Less extreme forms of siblicide are much more widespread in birds: usually the parent produces a hierarchy of chicks and, when conditions are less than perfect, the runt dies, either because its siblings passively deprive of it food, or through more direct attacks.