Begging behaviour and its energetic cost in great spotted cuckoo and magpie host chicks

Begging is one of the main factors governing food delivery to chicks by adu lt birds and it is of great importance in studies of biological communicati on theory. Many theoretical models have been proposed to explain the evolut ion of this noisy and conspicuous behaviour, all of which assume that beggi ng activity is energetically costly. We show that both great spotted cuckoo (Clamator glandarius) brood-parasitic chicks and magpie (Pica pica) host c hicks ceased to beg after ingesting enough food, and that great spotted cuc koo chicks emitted more begging calls and begged for much longer than did m agpie chicks. Using the doubly labelled water method to measure the daily e nergy expenditure of begging and nonbegging chicks in the laboratory, we sh ow that begging behaviour consumes only a small quantity of oxygen compared with other avian activities usually assumed to be energetically costly.