Thick eggshells of brood parasitic cowbirds protect their eggs and damage host eggs during laying

Abstract

Avian brood parasites have thick eggshells and numerous hypotheses have been proposed to account for the significance of this trait. We examined whether thick eggshells protect the eggs of the shiny and brown-headed cowbirds during laying events. We found that cowbird eggs were significantly less likely to be damaged compared to host eggs during laying events and, at the same time, these eggs also caused significantly more damage to host eggs.