Egg Size, Hatching Asynchrony, Sex, and Brood Reduction in the Common Grackle

摘要: In clutches of five, the Common Grackle (Quiscalus quiscula) provisions eggs un- equally and starts incubation before clutch is complete, thereby insuring initial advantages to some young which are not accrued others. Field observations experiments show: (1) egg wt increases with laying sequence within clutch, (2) intraclutch variation in size results competitive growth for from large eggs, (3) asynchronous hatching favors hatch early at expense those late, (4) starvation mediates brood reduction late-hatching many nests, (5) normal produces a sex ratio skewed favor 9 9. Egg interpreted as antagonistic forms parental investment. Presence both adaptations suggests that parent attempts ensure survival chicks late long possible an overall pattern investment ensures individual if food insufficient raise entire brood. This retention means by maximizes reproduction event unexpectedly favorable conditions. Elimination favoring because ultimately dependable exceptionally healthy, hence potentially polygynous, d cannot be produced. Facultative adjustment may produce high variance around population 1: 1 or kurtosis necessitated unequal costs raising individuals each sex. The this species evolved system reduces risks so maximize inclusive fitness.