It's probably an emperor penguin parent's worse nightmare: having to defend their chick from a kidnapper's attack. Sadly, on the occasions when a kidnap bid has succeeded, the kidnapper often abandons their victim several hours later. But what drives the kidnapper to such a fruitless act?Frédéric Angelier and colleagues wondered whether kidnapping behaviour might be caused by unusually high levels of the parenting hormone,prolactin, in penguin parents who have lost their own chick(p. 1413).

The team injected failed penguin parents with bromocriptine to artificially reduce the birds' prolactin levels and waited to see if the incidence of kidnapping declined too. Amazingly, the probability that a failed parent would stage an abduction fell 4.5 fold when their hormone levels were reduced. Although lowering the birds' prolactin levels hadn't abolished the behaviour,it had modified it.

But why do the failed parents maintain such high levels of prolactin when prolactin levels fall in other species that have lost their chicks, especially when the hormone has such drastic consequences? Angelier and colleagues suspect that the emperor penguins sustain high levels of prolactin to encourage them to return to their chick after a lengthy separation. Sadly,this incentive to come home after a long foraging trip seems to have a nasty side effect when parents return to find their chick gone.

Angelier, F., Barbraud, C., Lormée, H., Prud'homme, F. and Chastel, O. (
). Kidnapping of chicks in emperor penguins: a hormonal by-product?
J. Exp. Biol.