EVEN songbirds have their favourite offspring. Black redstarts can identify their chicks from differences in their pleas for food, enabling the parents to split the work of feeding the entire brood.
Tudor Draganoiu of the University of Leiden in the Netherlands and his colleagues spent three summers studying the interactions between black redstart (Phoenicurus ochruros) parents and chicks. They recorded the begging call of each fledgling and then played them back from carefully hidden speakers.
By observing the amount of parental interest in different begging calls, Draganoiu and his colleagues were able to show that parents divided up their broods, with each responding preferentially to the sound of particular chicks and feeding them more food. Often dad was lazier, feeding just one of the three to five chicks and leaving the rest to mum.
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Why do black redstarts divide up their brood in this way? One possibility is sexual conflict. 鈥淓ach parent may try to push the other to invest more than itself, saving as much energy as possible for future reproduction events,鈥� says Draganoiu, whose findings will be published in Animal Behaviour. Alternatively it could just be a more efficient way of rearing chicks: looking after two or three is easier than keeping your eye on five.
