Figure 1

Phenological variation in departure date from the wintering area (a), arrival date at the breeding site (b), and breeding date (c) of male (full symbols) and female (open symbols) barn swallows in relation to methylation at the poly-Q locus. Linear regression lines for males (dashed) and females (continuous) are shown. Dates are expressed as Julian day (1 = 1 January). See Table 1 for sample sizes.