The hoary bat cannot be mistaken for any other species. The tips of the hairs are white or grayish with brown shafts giving a frosty or hoary effect. The ears are short and round with a striking black border. This is one of Colorado's largest bats with a wingspan of about 400 mm, a body and tail about 140 mm long, and a forearm 50-58 mm long. Hoary bats weigh approximately 25 g.
Distribution: The hoary bat is widespread, ranging from northern Canada to Guatemala, and probably occurring in all states except Alaska -- even in Hawaii, where it is the only native land mammal. In Colorado, the hoary bat probably occurs statewide from the plains to timberline.
Habitat and Habits: The hoary bat is a solitary, tree-roosting species and can be expected to live in any habitat with trees. It is migratory with the sexes migrating north together in spring. During summer, the sexes separate, however, perhaps to reduce competition for food while females give birth and rear the young. Hoary bats arrive in Colorado in April and are gone by November. There is no record of hibernation here.
Breeding: Most females give birth and raise their young in northern and eastern North America, although a few females rear young in Colorado. Litter size is generally two with a range of one to four. Birth occurs between May and July. The mother can forage with the young clinging to her nipple, but generally the young are left at the roost site. Young begin to fly at about 30 days of age. Copulation usually occurs during the fall migration but may take place on wintering grounds. Implantation of the new embryos is postponed until spring when growth and development are completed.
Food: The hoary bat prefers moths but also feeds on beetles, wasps, grasshoppers and even small bats. An open-air forager, the animals seem to approach moths from the rear, severing the abdomen and thorax from the rest of the body. Flight is swift and direct, and a keen observer can readily identify the hoary bat by its flight pattern, body size and relatively long, narrow wings. It tends to emerge later in the evening to forage than most other local bats. In Colorado its foraging period seems to be varied, however, due to the vagaries of local weather. The hoary bat can often be seen foraging with the big brown bat near street lamps or other outdoor lights.
Remarks: Little is known about the natural history of this species in Colorado; it deserves more study.