Male Competition in Large Groups of Wintering Humpback Whales

Fast moving groups containing three or more adult humpback whales are found in the winter on Silver Bank in the West Indies, and off Hawaii. Many of these groups have a definite structure: a central Nuclear Animal, with or without a calf, is surrounded by escorts who compete, sometimes violently, for proximity to the Nuclear Animal. This competition involves fluke thrashes, the blowing of bubblestreams, and physical contact, some of which appears designed to hurt an opponent: bleeding wounds are seen on the competing escorts. Escorts sometimes leave these groups and start singing, and singers sometimes stop to join large groups. The pattern of interactions strongly suggests that the escorts are males competing for access to a central female. Off Hawaii singers respond to such groups at ranges of up to approximately 7.5 km. On Silver Bank, Principal Escorts maintained a position of closest proximity to the Nuclear Animal for an average of 7.5 hours before replacement.