Seasonal Changes in Clutch Size in British Birds

In many species of birds the mean clutch size is not constant through the breeding season: Some species show a seasonal pattern of declining clutch size, while others can show a mid-season peak. We suggest an evolutionary interpretation of the different patterns of seasonal change in birds, and test predictions by analysis of nest-record data held by the British Trust for Ornithology (BTO). We assume that conditions for breeding will show a seasonal pattern of improvement and then decline, and that the optimal clutch size (Lack 1947) is larger for each individual in the population when the conditions for breeding are better