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The language of birds: 2.2 Calls of young birds

We come now to calls used in "conversations" between young birds and their parents.
One of the more appealing bird recordings in the BBC Natural History Sound Archive was made in Suffolk in May 1972 by Eric Simms. He had placed a microphone by the nest of a stone curlew Burhinus oedicnemus (a bird that lays its eggs on bare ground). The clutch of two eggs were due to hatch but were as yet "unpipped". From inside each egg the chick could be heard calling; and the mother-to-be was also heard answering. Stone curlew chicks (like those of hens and ducks and many others) hatch in a well-developed state and can run from day one. There is thus the possibility that they will stray as the mother leads them away to suitable feeding areas. The vocal exchanges between "egg" and adult may have been arranged by natural selection so that offspring and parent can learn each other's voices before the young are mobile, and thus stand a better chance of finding each other when in thick ground vegetation. For species of wild duck that may have broods of 10, 12 or more, the problem of keeping together would be even greater.

Sharp clicking sounds from inside the unhatched eggs of various domestic and other bird species was long known to indicate the imminence of pipping and was believed to be due to tapping by the embryo against the shell. The sound is now known to be neither tapping nor vocalising, but a clicking associated with the ventilation of the lungs. The sound occurs rhythmically as the embryo breathes, and it is this sound which functions to coordinate the synchrony of the hatch. This is also important if the parents of young birds active from birth are not to lose their brood numbers. In this way all the young are ready to move off together. To this end, the 16 eggs laid by a grey partridge Perdix perdix, the 12 by a mallard Anas platyrhynchos, or the eight by a quail Coturnix coturnix (in each case one egg daily) are not warmed for the purpose of incubation until after the laying of the last one. Even so, experiments with the quail show, they would be likely to hatch over a period of up to 48 hours, meaning that the first chick out would need to wait two whole days for the last of the brood to appear. Amazing though it may seem, this problem is overcome by the embryos communicating with one another from inside the eggs, to arrange a near-simultaneous hatch which is completed within a period of - at most - six hours.

Listen
Herring Gull Larus argentatus
sounds of chick in egg before hatching, recorded by Richard Ranft, 21 May 1986, Skokholm Island, Dyfed, Wales.

Parent birds of species that hatch helpless young needing intensive care, are stimulated to feed their offspring not only by brightly coloured gape patterns flashed at them by hungry young, but also by begging cries. Youngsters as varied as chaffinches and great spotted woodpeckers Picoides major, kingfishers Alcedo atthis and golden eagles Aquila chrysaetos, appeal vocally for food.

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