Sex-Ratio Adjustment in the Common Grackle

Abstract

From the nestling period through maturity, female grackles are distinctly smaller than males and presumably cost less to rear. Individual birds nesting early in the season lay more female eggs than those nesting later, and in large broods, mortality after hatching consistently favors female fledglings. The first result suggests an adaptive nonrandom meiosis that anticipates seasonal conditions of food availability; the second implies a brood reduction strategy consistent with Fisher's prediction that differential mortality in sexually dimorphic species should favor the less expensive sex.