Social Behavior on the Winter Grounds
The Phenomenon of the "Escort"
Early work at KBMML identified the phenomenon of mother-calf pairs frequently accompanied by a third whale that typically trailed behind the pair or remained to one side or the other (Herman & Antinoja, 1977). We dubbed this whale the "Escort." Escorts have since been found to be males either through direct observation of the ventral surface of a whale or through genetic analysis of skin samples (e.g., Clapham, Palsboll, Mattila & Vasquez, 1992; Glockner, 1983). Escorting behavior is conducted by males towards females both with and without calves. The escort provides no parental care for a calf, but rather is seeking mating opportunities with the adult famales. TDI research has demonstrated that male humpbacks prefer to escort females without calves over females with calves, most likely because females without calves have a higher reproductive potential over females with calves (Craig, Herman, & Pack, 2002). When more than one escort is present, the males often compete, sometimes aggressively, for the position closest to the female. The male in this location is termed the "Principal Escort" (e.g., Tyack & Whitehead (1983). Thus, male humpacks are both choosy and competitive (Craig et al. 2002).Aggressive Behavior Between Male Humpbacks
As we and others studied humpback whales in the Hawaiian winter grounds, the popular labeling of these whales as "gentle giants" was brought into question. Whales were seen with heavily scarred bodies, ragged dorsal fins, and with tubercles on their head bleeding, all clearly the result of vigorous aggressive contacts between whales (Baker & Herman, 1984). The "competitive group", characterized by multiple escorts aggressing against one another to establish and maintain proximity to the lone female in the group, was seen as the locale where these bruises and scarring occurred.
Perils of Male-male Competition
The interaction occurring among males in competitive groups often involves body strikes, resulting at times in bleeding rostral tubercles and dorsal fins and body scarring. However, fatalities have not been observed previous to our observation in 1996 of a male humpback that had died while interacting within a competitive group. The dead animal was seen floating at the surface and was being attended by one or more of the males that had been in the group. One male wrapped its pectoral fins around the dead whale in a way that seemed to have both succorant and sexual components. Unfortunately, no necropsy could be performed to pinpoint the cause of death. (Pack et al. 1998).
Transient Affiliations of Males and Females
Escorts may remain with a mother-calf pair for only a matter of
hours, and may be seen at a later time or date with a different
mother-calf pair (Mobley & Herman, 1985). Similarly, particular
mother-calf pairs may be affiliated with different escorts, each
for a relatively short time, often on the order of hours. The social
matrix can then be described as fluid, and the escorts as prospecting
among multiple females, possibly for detection of receptivity to
mating.
Baker,
C. S. and Herman, L. M. (1984).
Aggressive behavior between humpback whales (Megaptera novaeangliae)
wintering in Hawaiian waters. Canadian Journal of Zoology 62,
1922-1937.
Clapham, P. J., Palsboll, P. J., Mattila, D.
K., & Vasquez, O. (1992). Composition and dynamics of humpback
whale competitive groups in the West Indies. Behaviour
122, 182-194.
Glockner, D. A. (1983). Determining the sex
of humpback whales Megaptera novaeangliae in their
natural environment. In R. S. Payne (ed.), Communication and
behavior of whales, Westview Press, Boulder, CO. pp. 447-464.
Herman,
L. M. and Antinoja, R. C. (1977). Humpback whales in the Hawaiian
breeding waters: Population and pod characteristics. Scientific
Reports of the Whales Research Institute (Tokyo)
29, 59-85.
Mobley,
J. R. and Herman, L. M. (1985). Transience of social affiliations
among humpback whales (Megaptera novaeangliae) on the Hawaiian
wintering grounds. Canadian Journal of Zoology 63, 762-772.
Pack, A.
A, Salden, D. R., Ferrari, M., Glockner-Ferrari, D., Herman, L.
M., Stubbs, H. A., & Straley, J. M. (1998). Male humpback whale
dies in competitive group in Hawaii. Marine Mammal Science 14,
861-873.
Tyack, P., and Whitehead, H. (1983). Male competition
in large groups of wintering humpback whales. Behaviour
83, 132-154.
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