The species is insectivorous and migratory. It is poorly known, however Hoary Bats are thought to prefer trees at the edge of clearings, but have also been found in trees in heavy forests, open wooded glades, and shade trees along urban streets and in city parks (Anderson 2002). They roost 3 to 5 m above ground during the day, usually in the foliage of trees. They prefer dense leaf coverage above and an open area below. They also prefer trees that border clearings. They have been seen roosting in a woodpecker hole in British Columbia, in the nest of a gray squirrel, and under a driftwood plank. Occasionally they are found clinging to the overhangs of buildings and in caves in the latter part of the summer. They often have trouble finding their way out of the caves and die there (Anderson 2002).

Hoary Bats reach their peak activity at about five hours after sunset, although they may occasionally be seen flying on warm winter afternoons. Their flight is strong and direct, reaching speeds of thirteen miles/hr. While hunting, they soar and glide. They forage about the tree tops, along streams and lake shores, and in urban areas where there are lots of trees. These bats stop to rest between meals at night. Hoary bats are solitary and feeding is the only time that they appear to associate with other bat species. Hoary bats often form groups when hunting for insects (Anderson 2002).

The species is widely distributed. It occurs in Colombia and Venezuela; Central Chile, Bolivia, Uruguay, Paraguay, and Central Argentina; Hawaii (USA); Guatemala and Mexico throughout the USA to Southern British Columbia, Southeastern Mackenzie, Hudson Bay and Southern Quebec (Canada); Galápagos Islands (Ecuador) (Simmons 2005); Panama (Samudio pers. comm.) and also in Brazil.

Because of its very extensive distribution in the Americas, this species is found in several protected areas through its range. However, most of the available studies are focused on North American populations, and very little is known on rost ecology, diet, reproduction, and taxonomic status of southern populations. For example, South American populations have been considered to represent one or two subspecies (Shrump and Shrump 1982), and the Hawaiian populations remains a mystery in term of its taxonomic status. Roosting ecology is a key factor for this species, but most of what is known comes from studies in North America only.