Interactions of singing humpback whales with other males

Two non-mutually exclusive hypotheses on the function of the humpback whale song are: (1) it attracts females to the male singer; (2) it is a male-mal e display, that may order status. To evaluate these, from 24 January-13 Apr il 1997 off Maul, Hawaii, 42 singers were located, audio-recorded, photo-id entified and monitored for interactions with other whales. Whales that join ed singers were biopsy sampled for molecular determination of sex. In 76% ( 32 of 42) of the interactions, a lone non-singing adult joined the singer. In the remainder, singers stopped singing and joined a nearby group or acco mpanied other whales. In 81% (26 of 32) instances where a lone adult joined a singer, the pair split again within minutes; otherwise a group formed. I n one such group the pair became a trio and eventually joined a competitive group. Behavior in joining/splitting interactions ranged from a single pas s-by, to surface activity such as tail lobs and breaches. The sex of 22 joi ners was determined: 14 genetically and eight behaviorally, All were males. Humpback whale song preceded, and at times followed, male-male interaction s of variable duration and agonistic level in and around the breeding seaso n. If considered within the context of a proposed dominance polygyny mating system, these observations appear to support speculation that the song may function in male social ordering.