Composition and dynamics of humpback whale competitive groups in the West Indies

• Published in: Behaviour
• Main Authors: Clapham, P J, Palsboll, P J, Mattila, D K, Vasquez, O
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1992
• Subjects: MEGAPTERA-NOVAEANGLIAE; BEHAVIOR; COOPERATION; COALITIONS; DOMINANCE; Humpback Whale; Megaptera novaeangliae
• Online Access: https://hdl.handle.net/11370/491f8e2b-a29b-45f3-9c76-bfad4df705c9; https://research.rug.nl/en/publications/491f8e2b-a29b-45f3-9c76-bfad4df705c9; https://doi.org/10.1163/156853992X00507

It has been hypothesized that humpback whale, Megaptera novaeangliae, competitive groups represent intrasexual competition by males for access to a mature female. The composition and dynamics of these groups was studied between 1989 and 1991 in Samana Bay, West Indies. The sex of group participants was determined by molecular analysis of skin biopsies. Groups showed similar characteristics of size and movement as those described from other breeding areas, except that only one group contained a calf. The sex was determined of 141 participants in 44 competitive groups. In 21 of these groups, we were able to biopsy all participants. No group contained more than one female, but seven of the wholly sampled groups (all of them small) consisted entirely of males. Of 22 animals who were ''positively'' assigned the role of Nuclear Animal, 17 were female, and five were male. Similarly, of 24 biopsied Principal Escorts, 23 were male and one female. All 24 biopsied Challengers were male. Of 55 animals who were either classified as Secondary Escort, or whose role could not be categorized, 51 were male and four female. In 8 cases, associated pairs of males exhibiting no aggression towards each other were observed to either enter or leave a competitive group together. Of 16 individuals resighted on more than one day, all but one were males. These data suggest that: 1. While most groups (as predicted) represent male-male competition for a single female, observers should be cautious in their assumptions; 2. All-male groups may represent dominance sorting by unfamiliar conspecifics; 3. Females may occasionally aggressively repel advances by unwanted males; 4. While unlikely in light of present knowledge, the possibility that males form coalitions cannot be dismissed. We suggest that competitive groups may be asymmetrical contests in which a female Nuclear Animal is of more value to the Principal Escort than to a Challenger, particularly if the former's defence of her represents mate-guarding.