Often female humpbacks will be accompanied by a male known as the escort. The escort position is prized, and competition for this prime mating right is common. When another male tries to un-seat the escort, he’s known as the challenger.
From time-to-time the escort/challenger competition escalates into a chase, and the frenzied activity draws in more whales from the surrounding area in to a heat run. A heat run can grown into a train of many animals– commonly 4-6 males plus the lead female, but they have been know to grow into larger pods. The largest number Darren has caught in one frame is 13 whales.
It’s within the heat run that dominance and hierarchy is sorted out, with the challenger aggressively attacking the escort and the escort defending his position, blowing bubble trails and using their bodies as weapons against each other. Other whales following along fight amongst themselves, but it’s believed that this is really just practice for when they decide they are dominant enough to be ready to challenge at some point in the future.