In several animals such as deer, sheep, and caribou in which newborns remain dependent on their mothers beyond birth, mothers often segregate themselves and their offspring into habitats that differ from those they use when without offspring. The motivations underlying such changes can range from predator avoidance to promotion of mother-offspring bonding to avoidance of male harassment. In two of our most recent scientific publications, we have been investigating how humpback whale females change their habitat preferences in Hawaiian waters based on their reproductive condition and on the age and size of their newborn calves. Published in 2018 in the journal Marine Mammal Science, our most recent study used our archival humpback whale tail fluke catalog to examine the habitat preferences of individually-identified females photographed off Maui in years when with a calf and years when without a calf. Thirty-five females were sighted across years in both types of reproductive conditions. We found that in the years when a female was a mother to a newborn calf, she was in shallower water than when she was without a calf. In the companion paper, published in 2017 in the journal Animal Behaviour, we measured the lengths of 96 humpback whale calves in waters off Maui as well as the water depth they occupied with their mothers. We found that larger calves were found with their mothers in deeper waters than smaller calves, even when time of season was accounted for. We also examined the habitat preferences of 72 mother-calf pairs who were resighted over various intervals within a breeding season. We found that as a calf aged, it tended to be found in deeper waters with its mother. Interestingly, we also found that when mother-calf pairs were in deeper waters they had a preference for rugged seabed terrain. We suspect that this kind of terrain provides more ‘acoustic camouflage’ from males than does flat terrain in the sense that it tends to be noisier from snapping shrimp. This might help mothers avoid harassment from males seeking mating opportunities by making it less likely that they are overheard communicating with their calves. This final bit is very intriguing as it may indicate a strategy evolved in mothers for mitigating male harassment while preparing (in deeper waters) for emigration back to the feeding grounds.
Full details of these TDI publications is as follows:
- Pack, A. A., Herman, L. M., Craig, A., Spitz, A., Waterman, J., Herman, E., Deakos, M., Hakala, S. & Lowe, C. (2018). Depth and seabed terrain preferences of individually identified female humpback whales (Megaptera novaeanagliae) in relation to their reproductive state. Marine Mammal Science, 34, 1097-1110. DOI:10.1111/mms12495
- Pack, A. A., Herman, L. M., Craig, A., Spitz, A., Waterman, J., Herman, E., Deakos, M., Hakala, S. & Lowe, C. (2017). Habitat preferences by individual humpback whale mothers in the Hawaiian breeding grounds vary with the age and size of their calves. Animal Behaviour, 133, 131-144.