Relationship between female and male attentiveness in species with biparental incubation ( N = 124). Full line is ordinary linear regression fit whereas dashed line is phylogenetically corrected fit based on population-level analyses. Dotted lines connect points with identical total nest attentiveness. Inspection of the two regression lines (especially their crossing with dotted lines of equal total attentiveness) suggests that at lower total attentiveness (ca. 70%) female contribution is much higher than male contribution, whereas at higher total attentiveness (ca. 90%) sex-specific contribution is more equal.