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Energy expenditure of adult Pied Kingfishers was measured with doubly-labeled water. Results were related to reproductive success of parents aided and unaided by helpers. Energetically stressed parents in a colony with poor food supply accepted potential helpers more often than unstressed birds in another colony where food was easily available. This treatment of helpers was reversed in both colonies through experimental manipulation of clutch size and hence energetic stress. Results are discussed in relation to the costs and benefits that helpers incur on the parents' fitness.