The food requirements of dependent sons and daughters have important implications for evolution of the sex ratio, according to current sex allocation theory. We studied food requirements of nestling American kestrels (Falco sparverius), a moderately size-dimorphic falcon, by hand-feeding 61 birds from hatching to fledging. Daughters, the larger gender, consumed 6.99% more food than did sons. Sons did not have higher energy expenditure from higher effort during sibling competition than daughters did, so parents must supply more food to satisfy daughters' needs than to satisfy sons'. A review of all related studies shows a strong positive association between the degree of sexual size dimorphism and gender difference in food requirements.