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hoary bat

hoary bat (Aeorestes cinereus)
Photo © Michael Durham

Features and Behaviors

An adult hoary bat is very large with a body length of five inches and a forearm two inches long. Its brown-black hair has white on the tip. The belly fur is not frosted but is lighter than the back. The top of the tail is heavily furred. Brown fur extends on the underside of the wing to near the wrist.

The hoary bat may be found statewide as a migrant in Illinois in spring and fall, although some females do remain in the state in the summer. It is absent in the winter. The hoary bat lives in trees. It eats insects. It is a solitary bat that becomes active late after sundown. This bat flies quickly and in a straight line. Mating occurs in the fall, winter or spring. Those females that mate in the fall or winter store sperm in the uterus until spring, when it is used to fertilize the eggs. Young, usually two per female, are born in May and June. The female may take the young with her while she forages, but this practice stops when the young are about one week old. The hoary bat migrates north through Illinois in April and May. The southward migration occurs in the fall and is completed by November.

Illinois Range


​Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Chiroptera
Family: Vespertilionidae

Illinois Status: common, native