Although they ranged far south during the Wisconsinan, the onset of warm conditions shrank their range toward the north, and have only recently reclaimed their former American ranges because of human-induced environmental changes.
Aínda que chegaron moi ó sur durante o período de Wisconsin, o inicio das condicións cálidas encolleu o seu alcance cara ó norte e recentemente recuperaron os seus antigos hábitats americanos grazas a cambios ambientais inducidos polo ser humano.