A Note on Suckling Behavior and Laterality in Nursing Humpback Whale Calves from Underwater Observations.

Abstract

Simple SummaryNursing in large baleen whales and specifically the humpback whale is not well documented and difficult to capture in real time. Using underwater video documentation techniques, we collected digital video footage of humpback whale nursing events. From this, we provide an enhanced descriptive account of humpback whale suckling and recorded milk in the water near a nursing mother and calf column for the first time. As part of our investigation into nursing behaviors, we assessed if humpback calves demonstrated any patterns of laterality during nursing events. A pattern of laterality was noted in that all suckling events had a right side bias. Nursing bouts were short and intermittent, which coincides with what is known of larger terrestrial mammals such as the African elephant and other baleen whales. These shorter nursing periods are likely are due to the energetics of baleen whale milk coupled with the calf′s short respiration cycle before it has to return to the surface to breathe. Our study shows that underwater observations in marine mammal science provide valuable insight into real time events not easily accessible from vessel or aerial platforms.We investigated nursing behavior on the Hawaiian breeding grounds for first year humpback whale (Megaptera novaeangliae) calves. We observed and video-documented underwater events with nursing behavior from five different whale groups. The observed nursing events include behaviors where a calf positions itself at a 30–45° angle to the midline of the mother’s body, with its mouth touching her mammary slit (i.e., suckling position). On two occasions, milk in the water column was recorded in close proximity to a mother/calf pair, and on one occasion, milk was recorded 2.5 min after suckling observed. Nursing events, where the calf was located in the suckling position, were found to be short in duration with a mean of 30.6 s (range 15.0–55.0, standard deviation (SD) = 16.9). All observations of the calf in the suckling position (n = 5, 100%) were with the calf located on the right side of the mother, suggesting a potential for right side laterality preference in the context of nursing behavior. Our study provides insight into mother/calf behaviors from a unique underwater vantage. Results supplement previous accounts of humpback whale nursing in Hawaiian waters, validate mother/calf positioning, document milk in the water column, and introduce the potential for laterality in nursing behavior for humpback whale calves.