Energetic constraints on clutch size and time of breeding in temperate zone birds.

A model for the energy budget of a breeding pair of Great Tits is synthesized from published data. The model is used to investigate the relationship between temperature, clutch size, onset of laying, and male feeding on breeding success. Two periods of energetic stress are found, one at the end of the incubation period which is independent of the clutch size, and one at the end of the fledging period which does depend upon the clutch size. This energetic bottleneck theory is easily testable and is in agreement with existing data. The model also provides a consistent explanation of the effects of reduced male feeding, and changes in clutch size and nest box insulation on breeding success.