Hatching asynchrony and fitness in a neotropical seabird: second-hatched individuals from highly asynchronous broods are less fit but only during the rearing period

Early-life conditions are important determinants of phenotype and fitness. In birds, hatching asynchrony can generate differences in early-life conditions within a brood, which, in turn, can have far reaching fitness consequences for offspring, particularly so for later-hatched nestlings. A plethora of literature has examined consequences of hatching asynchrony during the nestling phase; however, long-term effects remain poorly understood. Using a 33-year population study of the Blue-footed booby ( Sula nebouxii ) off the Pacific Coast of Mexico, we show that the level of hatching asynchrony affects early- life survival of second-hatched nestlings. Junior boobies from highly asynchronous broods died at younger ages during the rearing period and were less likely to fledge compared to first-hatched offspring. However, level of hatching asynchrony did not have long-term fitness effects on either senior- or junior juveniles or adults. Our results provide insight into how parentally imposed natal environments affect early-life survival and late-life fitness traits in a long-lived seabird. Highlights Parentally imposed natal conditions can have far reaching fitness consequences for offspring. In birds, hatching asynchrony can produce size hierarchies within a brood. The effects of natural variation in hatching asynchrony on fitness is poorly understood. High levels of hatching asynchrony are detrimental for junior booby nestlings. Hatching asynchrony does not affect fitness in the juvenile or adult periods.