The energetic cost of begging behaviour in nestling house wrens

This study presents data relevant to the hypothesis that the energy expenditure associated with begging influences the signalling of need by nestling birds. We used open-circuit respirometry to measure the energy costs of resting, begging and non-begging activities in nestling house wrens, Troglodytes aedon, ranging in age from 1 to 11 days post-hatching. Across all ages, begging caused a 27% increase in metabolism above resting rates. The metabolic rate during begging was not related to begging vigour. However, more vigorous begs were longer and so required a greater total energy expenditure. We analysed videotapes of broods for nestling behavioural time budgets which were combined with the metabolic data and data on growth at different ages to generate daily energy budgets. Over a 24-h period, the cumulative energy allocated to begging was slight, ranging from 0.02% of the energy budget in younger nestlings (3 days old) to 0.22% in older ones (10 days old). In contrast, non-begging movements accounted for 2 and 9% of the daily energy budget of younger and older nestlings, respectively. Relative to daily growth, the energy allocated to begging was equivalent to 0.05% (younger nestlings) and 2.3% (older nestlings) of the energy sequestered in new tissue, whereas the values for non-begging activities were 5.1 and 96.8%, respectively. These results suggest that the energetic cost of begging is not likely to have a substantial role in influencing communication of need by nestlings. (C) 1998 The Association for the Study of Animal Behaviour.