Experiments on birds, fish and mammals have shown that adverse conditions during infancy can produce diverse long-term and delayed deficits during adulthood, prejudicing both the individual and its offspring. Natural selection should prepare animals to cope with adversity of the type, magnitude and timing that commonly occur in their natural habitat, but very little is known about such evolved developmental buffering against natural ‘poor starts’ in life. In two-chick broods of the blue-footed booby Sula nebouxii, the junior (younger) chick usually experiences aggressive subordination, reduced nutrition and growth and elevated circulating corticosterone. To test whether this poor start produces long-term, delayed or intergenerational deficits in body size, body condition or cell-mediated immune response, we measured 3–8 yr old female breeders banded as chicks, and their infant offspring. Results failed to support our predictions. Compared to former seniors and former singletons (solitary nestlings), former juniors showed no deficit in cell-mediated immune response at any age. They showed an 8.04% deficit in body condition at age 4–6 yr but this deficit disappeared completely by age 7–8 yr. Furthermore, their offspring showed no deficits in body size, body condition or immune response. Junior chicks are affected by their poor start, but their developmental resilience, also confirmed by studies of post-fledging survivorship, recruitment, natal dispersal, aggressive nest defense and reproduction, is evidence of evolved developmental buffering against predictable adversity during infancy.