Some humpback whales migrate annually from Antarctic feeding grounds to the seas around the Tongan Islands to give birth and mate. The Tongan humpbacks are considered part of Southern Hemisphere Group V that splits during migration, some swimming to Eastern Australia and others to various Polynesian Islands. During this time long complex songs are produced. The song is thought to be a male breeding display and may serve either as an intra-sexual or an inter-sexual signal or both. It is in a constant state of change that occurs every season. Since these changes are directional they cannot be described by drift, and singers incorporate changes as they occur, thus song must be shared through cultural transmission. This investigation describes the cultural changes that occurred in 158 songs recorded from Tongan humpbacks through the 1990s. The rate of change differed within years, some themes were retained for as much as five years and others were lost after only two years. The farther apart the years the less similar are the songs, as in the humpback songs of the Northern Hemisphere. The largest number of changes seems to have occurred in the early 1990s where all themes seemed to have been lost and new ones originated. What initiates these changes remains speculative, but we assess some hypotheses in relation to humpback whale behaviour and cultural transmission in avian song. ?? Koninklijke Brill NV, 2005.