Intersexual Differences in Food Consumption by Hand-Reared Great-Tailed Grackle (Quiscalus mexicanus) Nestlings

I monitored food consumption by hand-reared Great-tailed Grackle (Quiscalus mexicanus) nestlings to test the hypothesis that males and females consume similar amounts of food but males direct more of their energy into characters that result in greater mass increase. Growth patterns of hand-reared nestlings reflected those of naturally reared nestlings: males were heavier and had longer tarsi, and females had longer 9th primaries on days 6-12 post-hatching. Males, on average, consumed 15.8% more food than females throughout this period; the amount of food consumed per unit mass increase was similar for both sexes. The results suggest there may be substantial cost differences to parents in rearing offspring of different sex. The nestling sex ratio for this and other sexually size-dimorphic species is generally close to one, and Fisher's (1930) theory that differential investment in sons and daughters should result in a skewed sex ratio at the end of parental care is not supported.