Spring migration can begin as early as late March, but most Indiana bats do not leave their winter hibernacula until late April to early May. Females emerge from hibernacula first, usually between late March and early May. Most males do not begin to emerge until mid- to late April. Females arrive at summer locations beginning in mid-April. Females form summer nursery colonies of up to 100 adult females during summer. Males typically roost alone or in small bachelor groups during the summer. Many males spend the summer near their winter hibernacula, while others migrate to other areas, similar to areas used by females.