Figure 1. Mean (+ s.e.) breeding date of the genotypes in the sex by age classes of the barn swallow.

Numbers in the body of the graphs are sample sizes. Breeding date data of the single Q₇/Q₈ older female or male (denoted by 1*) are reported for completeness but are not included in the statistical analyses. The difference between yearling female Q₇/Q₇ and Q₇/Q₈ was significant (P < 0.05, see Results).