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. HighlightsO_LIParentally imposed natal conditions can have far reaching fitness consequences for offspring. C_LIO_LIIn birds, hatching asynchrony can produce size hierarchies within a brood. C_LIO_LIThe effects of natural variation in hatching asynchrony on fitness is poorly understood. C_LIO_LIHigh levels of hatching asynchrony are detrimental for junior booby nestlings. C_LIO_LIHatching asynchrony does not affect fitness in the juvenile or adult periods. C_LI