Little Brown Bat
The most common bat in Wisconsin is the little brown bat. This bat is about 3-3.5 inches long with a wingspan of 8.5-10.5 inches. They will weigh about 0.25-0.35 ounces with the females slightly heavier than the males. Little brown bats can be found with a wide range of colors from almost black to a pale brown-gray. Often, a dark spot can be seen on the shoulder of the bat. Little brown bats eat a wide variety of flying insects including night-flying moths, bugs, beetles, flies, and mosquitoes. Insects are caught with the wing or tail membrane and “flipped” into the mouth of the flying bat. Little brown bats usually begin to feed just at dusk, after locating and taking a drink of water. Little brown bats begin hibernation in mid-October. They gather together in clusters on the cool cave ceiling to conserve body heat. The bats will wake from hibernation in late April or early May. Little brown bats return every year to the same cave or building to hibernate. Pups are born in mid-May or very early June in maternity or nursery colonies. Little brown bats give birth to one pup each year. The young pups grow rapidly and are able to fly in about four weeks. Little brown bats may live as long as twenty-five years.
Big Brown Bat
The big brown bat is approximately 4-5 inches long. It has a wingspan of about 12-13 inches and weighs 0.4-0.5 ounces. The bat’s fur is usually dark brown with the face, ears, and wing membranes a blackish color. Big brown bats can be found in the city or country. They like to roost in attics, barns, behind doors and shutters, and in hollow trees. Big brown bats fly at dusk and generally feed in the same area each night. They fly in a nearly straight line and quite often, you will hear them “chatter” while swooping for food. These are the last bats to enter hibernation usually in late October or mid-November but they may wait until December. They emerge from hibernation in late March or early April to begin feeding on bugs. Big brown bats give birth to two pups in June. They may live to be as old as twenty years.
Eastern Pipistrelle (Tri-Colored)
The eastern pipistrelle (tri-colored), fondly called the pip, is Wisconsin’s smallest bat, only about 2.5 to 3 inches long. The pip weighs only 0.14-0.25 ounces and has a wingspan of 8-10 inches. Pips are yellowish brown to silvery-brown. A unique color feature is the “pinkish” arm bone of the pip which helps to separate it from the little brown bat. Pips feed in the early evening looking for flies and grain moths. They spend summers in open woods, near water, cliff crevices, buildings and caves. Pipistrelles hibernate from September through May in caves with temperatures around 50 degrees. The pip is an extremely sound sleeper, seldom moving during the winter. It is a solitary hibernator, preferring to be alone rather than in clusters. Pipistrelles give birth to one or two pups in June. The littlest bats in Wisconsin live an average of 4-8 years but can live to be 15 years old. In Michigan, pips are considered a species of concern.
The northern myotis closely resembles the little brown bat in coloring, size, facial features and habitat. In most instances the only way to identify the northern myotis is by closely checking ear length. The ears of a northern myotis will be 0.55-0.75 inches long compared to only 0.43-0.63 inches for a little brown bat.