'Mum! I'm hungry!' Hungry chicks have unique calls to their parents

German and Swiss ornithologists studied the calls of chicks in a population of Jackson's golden-backed weaver birds on the shores of Lake Baringo in Kenya. Already knowing that parent birds can distinguish their own chicks from others by unique pattern changes in the frequency of their call, the researchers wondered how the parents could also tell if their own chick was hungry, and how hungry.

By temporarily removing chicks from their nests, the team set up cameras and microphones to record the chicks' behavior and begging calls. Lead researcher Hendrik Reers said, "Weaver bird chicks have two parts to their call; a "whistle-like" call followed by a "trill-like" call. In a non-hungry state, these parts of the call are slightly different from bird to bird,., and this allows the mother to identify their chicks. As the chicks get hungrier, as you might expect with any baby, the call gets louder and more energetic, but each bird still has a unique way of modifying their "normal" call to an "I'm hungry" call. These results imply that parents have to be familiar with their chicks' begging calls in order to estimate their hunger precisely."

The group found that the weaver bird chicks changed the length, pitch and amplitude of their begging calls, adding extra trills and shortening whistles. In fact, the hungrier a chick got, the more unique the call became. It seems that if you're a baby bird singing for your supper, the best way to make sure you get fed is to sing a different tune from everyone else!

More information: The effect of hunger on the acoustic individuality in begging calls of a colonially breeding weaver bird, Hendrik Reers and Alain Jacot, BMC Ecology (in press)

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