The two southern U.S. resident populations are somewhat more distinct. The Cuban population has been comparatively little studied, but appears to have been established on the island for a long time. They and the migratory greater sandhill cranes proper may form a group of lineages that diverged much later from a range in the southern U.S. and maybe northern Mexico, where they were resident. The southern migratory population would then represent a later re-expansion, which (re-)evolved their migratory habits independent from the northernmost birds, the geographically separated populations expanding rapidly when more habitat was available as the last ice age ended.