Supportive behavior of free-ranging Atlantic spotted dolphins (Stenella frontalis) toward dead neonates, with data on perinatal mortality

Abstract

This study adds the Atlantic spotted dolphin Stenella frontalis to the list of species displaying nurturant behavior as a response to perinatal mortality. It is based on two in situ behavioral observations off Madeira Island (Portugal) (but with only one continuing uninterrupted). Additionally, postmortem exams were carried out on four fresh neonate carcasses, two from the previous events and two from distinct events where carcasses were found floating with no individuals in the vicinity. The in situ observations show that adult Atlantic spotted dolphins try to support their dead calves at surface, either involving a single individual (presumably the mother) or several individuals. The highly fresh condition of the carcasses suggests that the adults abandon them after a short period of time (hours). The postmortem exams suggest that the four neonates died from natural causes, and not from anthropogenic causes, predation, or other intra- or interspecific behavioral interaction as described in some cetacean populations. Accurate lengths at birth are also provided, which are scarce in literature for this species.