Humpback whales (Megaptera novaeangliae) migrate annually between high-latitude summer feeding waters and low-latitude winter mating waters with a high degree of site fidelity. During migration and in winter waters, adult (male) humpbacks produce long complex songs. Song content is dynamic, but singers incorporate changes as they occur. Song sharing across regions is cultural, thus similarity of songs from different regions may be an index of reproductive isolation. Songs recorded in Tonga, New Caledonia, Eastern Australia, and Kaikoura, New Zealand, in the winter of 1994 are compared. The song from Kaikoura is the most southerly recording of song, over 2000 km south of winter migration termini. Seven themes were shared by all regions plus two themes not observed in Tonga. Differences in regional variants were most pronounced between Tongan and Eastern Australian song. New Caledonian and Kaikouran song were proportionately more like Eastern Australia. Kaikoura song was more similar to Eastern Australian song than Tongan song. These regional differences can be considered to be dialects that are maintained through cultural transmission of regional variants. The results suggest some migratory exchange among widely separate wintering regions of area V and speculation that song sharing occurs throughout migration and breeding seasons.