Humpback whale males exhibit several different agonistic behaviors when vying for access to a female. "Aggressive behavior between escorting males followed a roughly hierarchical scaling of intensity: interception and broadside display; head lunges (with increasing frequency, and ever closer); displacements; charge-strikes (butting, lateral fluke strikes, peduncle strikes)" (Baker 1984). Aggressive behavior also includes body thrashing, horizontal tail lashing, and lobtailing. Humpbacks that are in groups tend to be more aggressive than Humpbacks that are solo (Kurlansky 2000). "A seasonal peak in the frequency of aggression is probably related to an increase in population density and to changes in the reproductive physiology of mature males and females. Singing may function, in part, to synchronize ovulation in females with the peak abundance of mature males on the wintering grounds" (Baker 1984) (see Singing). Increased aggression during the breeding season may be physiologically spurred by the increased size of the testes, and increased amount of spermatogenesis (Kurlansky 2000), which likely causes an increased level of testosterone in males.

Humpback males have been known to cooperate during the breeding season in forming coalitions to gain access to females. "Within these competitive groups there is some evidence that related males may be present. For example, pairs of males have been seen to enter and leave the groups together, suggestive of a social bond which might be based on kin, and one pair moved between groups together and fought other males but never each other" (Valsecchi 2002).

With physical male-male competition, size offers a distinct advantage in gaining access to females (Spitz 2002). However, Humpback males are actually smaller than Humpback females, which is the opposite of what is expected. Humpback male singing may be another display or behavior that is more important than sheer size in determining reproductive success.

Humpbacks are not always antagonistic towards other Humpbacks. In the summer feeding grounds, groups of Humpbacks may exhibit cooperative feeding behavior. Data suggest that cooperative feeding groups are not composed of close relatives, so it is unlikely that kin selection is the reason for the cooperation (Valsecchi 2002). It could be that reciprocal altruism and selfish behavior are responsible. There are certain cases where one Humpback swam below a school and created a bubble-net to enclose the school, and then seven other Humpbacks swam through, gulping prey as they went. (D'Vincent 1985) This behavior could be considered reciprocal altruism, because in the short-term one whale is catching very little fish while others are benefiting by catching more. When the Humpbacks switch roles, then the first whale is reciprocated for his effort. However, not all cooperation is reciprocal altruism. In that same observation (D'Vincent 1985), bubble-net behavior was abandoned upon switching to new prey, and all the whales made synchronous vertical-lunges together. This cooperation could be immediately beneficial to all if more prey can be captured when the schooling fish become disoriented and incapacitated after one Humpback lunges through.

Group feeding is not always cooperative in Humpback whales. When a small group is feeding, they can probably catch as much prey by lunging through wherever the prey is densest, and avoiding areas that have already been strained by other Humpbacks (Watkins 1979). However, when the group becomes larger, the Humpbacks cannot simply avoid each other as they lunge through fish schools. There can be " apparent competition for food, with as many as 7 whales rushing to the surface, pushing and shoving as they went, raising their mouths out of water together in random orientation, and then falling back onto each other, mouth and throat full (of water at least)" (Watkins 1979). It is likely that cooperation would benefit everyone more, but it is likely difficult to organize cooperation in a pod that is so transient.

This web site was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2005.

All questions should be directed to the author, Austin Mercadante, aumercadante@davidson.edu