Benign Neglect of Terminal Eggs in Herring Gulls

Terminal-egg neglect arises in Herring Gulls (Larus argentatus) when parents begin to feed and brood the first two (a-, b-) newly hatched young, thereby disrupting incubation of the third (c-) egg. Mean temperature of pipped c-eggs dropped to 33.4°C, significantly below that of the pipped a- (37.6°C) and b- (36.6°C) eggs. Experimental manipulation of neglect by placement of pipped c-eggs at chronologically earlier nests showed that both hatchability and time to hatch were unaffected by natural levels of neglect. Laboratory incubation confirmed that chilling pipped eggs to 33°C does not affect hatching. Further chilling to 30°C lowered hatchability and increased hatching times. Development was arrested at 27°C. Although Herring Gulls clearly neglected terminal eggs during the final stages of incubation, it was entirely benign in that mean embryonic temperatures were maintained above levels that would cause damage. Last-hatched eggs in this species are evidently well-adapted, physiologically, to withstand chilling down to at least 33°C, thereby enabling them to maintain full viability despite moderate levels of neglect during the hatching period.