Nager R.G. (2006) The challenges of making eggs. ARDEA 94 (3): 323-346

Egg formation is a demanding process both in terms of energy and nutrient requirements. Birds must not only collect specific nutrients for egg formation, but must do so over a brief period when food may not yet be plentiful. Supplementary feeding experiments show that timing of egg formation and the number and quality of eggs formed can depend on energetic and nutritional factors, although they may not all be affected in the same way. Resources required for egg formation may come both from body reserves accumulated before egg formation starts and resource intake during egg formation. Egg formation is not only costly in terms of resource requirement, but variation in egg formation effort also has consequences on the bird’s fitness. Increased egg formation effort can lead to poorer body condition at the end of laying, poorer egg quality, reduced parental chick rearing ability and lower future reproductive success.