Behavioral ontogeny in humpback whale (Megaptera novaeangliae) calves during their residence in Hawaiian waters

The ontogeny of behavior in young offspring is a key component of a species life history, influencing short-term survival and life-long future fitness. In this study, we examine the behavioral ontogeny of humpback whale calves during their natal season on the winter breeding grounds. Behavioral data were collected during focal follows for 69 calves. Their relative age was estimated based on the degree of unfurling of the dorsal fin, and analysis of their time budgets revealed that behavior changed as the calves matured. Among the youngest group of calves (n= 27), persistent travel accounted for median 85% (interquartile range 34%) of the calves' time budget, they spent little time alone at the surface and the breathing regime included frequent intermittent breaths. Within the oldest group of calves (n= 26), time spent traveling dropped to a median 47% (IQR 42%) of the time budget, they spent more time at rest, surfaced alone more frequently, and the breathing regime more closely resembled that of adult humpbacks. We suggest potential functions for these and other components of calf behavior during this period, and review our findings in light of recent discussions on the role of predation pressure as a driving force in mysticete migration.