Behavior and Social Organization of Humpback Whale (Megaptera novaeangliae) Mother/Calf Pairs on a North Atlantic Feeding Ground
Katherine A. Sardi¹,², Mason T. Weinrich¹ and Richard C. Connor²
¹ The Whale Center of New England, PO Box 159, Gloucester, MA 01930
² Biology Dept. UMass Dartmouth, 285 Old Westport Rd., N. Dartmouth, MA, 02747
Several aspects of humpback whale (Megaptera novaeangliae) mother/calf social organization and behavior on the feeding grounds were examined in this study. Previously, little research has focused on humpback whale mother/calf pairs on their feeding and calf rearing grounds. Data were collected from 1984 to 1998 on Stellwagen Bank and Jeffreys Ledge, both within the Gulf of Maine. Humpback whale calves exhibited a significantly higher rate of aerial behavior, such as breaching, when separated from their mothers (Mann Whitney U test P < 0.001). Aerial behaviors created surface disturbance and are thought to have also created subsurface noise. The calf may have used this sound to communicate with or provide an acoustic locator for the mother. Simple play behaviors, such as spyhopping, occurred at a slightly higher, but not significant, rate when the calf was separate from the mother (Mann Whitney U test P=0.202). Play behaviors created a smaller surface disturbance, if any, and presumably very little subsurface noise. Mother/calf pairs associated with adults at a higher rate and for a longer duration than any other age class (ANOVA P=0.014). There was no significant difference in rate or duration of association between males and females (ANOVA P=0.842). Data were consistent between 1984 and 1997. However, during the 1998 field season, there was a dramatic increase in occurrence of groups containing more than one mother/calf pair. This increase coincided with an overall increase in group size, perhaps due to a unique method of prey exploitation.
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