Ontogeny of plunge diving behaviour in brown boobies: Application of a data logging technique to hand-raised seabirds

How do seabirds acquire diving skills after fledging? This is an important issue to complete our basic knowledge of life history in seabirds, but the mobility of juveniles obstructs the continuous recording of the development of diving behaviour. In this study, we raised hatchling brown boobies, Sula leucogaster, which are known to have a long post-fledging period. Once boobies began to fly, they made round trips between the sea and the nest, and begged for food from us, their surrogate parents. During this post-fledging care period, the development of diving behaviour was recorded using data loggers. In addition, we attached data loggers to adult brown boobies in the field and compared their diving performance with that of juveniles. The hand-raised juveniles had relatively slow development of diving ability during the first month after fledging. This slow development of behaviour with ontogeny might be the proximate cause for the extended post-fledging care period in this species. This study shows that the combination of bio-logging and hand raising of seabirds is a useful tool for assessing the ontogeny of diving behaviour in these animals.