SEXUAL SIZE DIMORPHISM AND FOOD-REQUIREMENTS OF NESTLING BIRDS

The food requirements of dependent sons and daughters have important i mplications for evolution of the sex ratio, according to current sex a llocation theory. We studied food requirements of nestling American ke strels (Falco sparverius), a moderately size-dimorphic falcon, by hand -feeding 61 birds from hatching to fledging. Daughters, the larger gen der, 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 s trong positive association between the degree of sexual size dimorphis m and gender difference in food requirements.