Time and energy constraints on the brood size of swallows, Hirundo rustica, and sand martins, Riparia riparia.

The daily energy requirements of swallow Hirundo rustica and sand martin Riparia riparia adults with broods of different sizes were compared with the energy (food) gain rates of adults. Energy requirements of broods were obtained from food delivery rates, growth rates and from published data. The energy requirements of adults were obtained from DO measurements and from time budgets.