Ontogeny and synchrony of diving behavior in Humpback whale mothers and calves on their breeding ground

Abstract

Abstract For humpback whales, the mother–calf pair is the only stable social unit with calves following their mother after birth and staying in close proximity. This following strategy ensures the maintenance of such close proximity between the mother and her calf, with calves benefiting from maternal protection and care. Using multi-sensor tags, we recorded the diving behavior of calves at three different age-classes (C1, C2, C3) to assess how calves developed in their natural environment at an early stage of their life. From 29 deployments on calves, we extracted the diving metrics from two C1 neonate calves, eight C2 calves, and 19 C3 calves, and we found that some diving metrics (dive duration, time at bottom, maximal depth, or maximal dive duration) differed among calves’ age-classes. On 23 tagged mothers, we analyzed if their diving profiles also varied depending on calf’s age-class. We showed that only two dive metrics of mothers varied with the age of their own calves (time spent at the bottom, and time interval between dives), but all others were not reliant on the calf’s age. Simultaneous deployments on seven mother–calf pairs in 2016 and 2017 revealed highly synchronized dives, with mothers leading the diving pattern. This work represents an extensive study investigating the diving behavior in humpback whale mother–calf pairs on their breeding ground.