Social interactions of humpback whale (Megaptera novaeangliae) mother/calf pairs on a North Atlantic feeding ground

Abstract

We examined the association patterns and relative positioning of whales in groups containing a mother/calf pair in the southern Gulf of Maine between 1984 and 1998. We defined association patterns based on associate age and sex class, and the mother's reproductive history. Mother/calf pairs had an overall preference for adult males. In years when the same females were not accompanied by a calf, they had a preference for adults of either sex and male sub-adults (whales between five and seven years of age). We also compared associations of females combined for all years that they had calves versus years without a dependent calf and found distinct differences. In years with and without a calf, females often associated with adult males. However, in years with a calf, there was an increase in association with juvenile males and in calf-less years, there was an increase in associations with adult females. The reproductive history of the mother did not seem to impact her associations; analysis of association patterns of mothers with varying reproductive parameters did not yield significant results. Mothers were positioned between the calf and associates in the group significantly more often than expected, both in duration and surfacing frequency. However, the relative positions of individuals in the group were not fixed; they were fluid and shifted often. Interactions between mother and juvenile associates sometimes appeared antagonistic, with the juvenile attempting to place itself next to the calf and the mother blocking its approach. Our data demonstrate that mother/calf pairs, while less social than other humpback whales, have specific social patterns when on their feeding grounds.