IMAGINE trying to hear your mother鈥檚 voice in a crowd of a million shouting people. This is the task facing king penguin chicks. But mum鈥檚 calls are cleverly designed to help junior.
Adult king penguins make a series of four to eight calls, which each go from loud to soft and are composed of numerous harmonics. Previous tests have suggested that the chicks don鈥檛 need the loud-soft component or the harmonics to recognise their mother鈥檚 calls. So why the complexity?
Thierry Aubin at Paris South University and Pierre Jouventin at the Functional and Evolutionary Ecology Centre in Montpellier tested chicks on Possession Island in the Antarctic. They found that while the baby birds could recognise their mothers even from recordings with the extra bits removed, all of the acoustic components were vital for them to locate calls amid the din of the colony (Journal of Experimental Biology, vol 205, p 3793). Most chicks also needed to hear at least three calls before setting off in the direction of their mothers.
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