Are Parents Okay with Sibling Bullying?

Abstract

Abstract According to inclusive fitness theory, blue-foot parents should sometimes enter into conflict with their senior chicks over food allocation between chicks and the killing of junior chicks, but extensive observation revealed no clear examples of such parent–offspring conflict. Seniors exercise this selfish control of their siblings with restraint, and parents do not restrain seniors’ aggressive dominance, privileged feeding, or siblicidal harassment of juniors. We looked for signs that fundamental parent–offspring conflict has been resolved by the evolution of subtle parental strategies to defend the interests of juniors. There was no clear evidence of mothers influencing sibling conflict by differentially supplying their first and second eggs with hormones or yolk, by fine-tuning the age difference between siblings, or by controlling the hatching order of female and male chicks. Parents and seniors may have coevolved to entrust control of juniors’ feeding and survival to seniors because their conflict of interests is minor.