The tricolored bat or American perimyotis is a species of microbat native to eastern North America. Formerly known as the eastern pipistrelle, based on the incorrect belief that it was closely related to European Pipistrellus species, the closest known relative of the tricolored bat is now recognized as the canyon bat. Its common name "tricolored bat" derives from the coloration of the hairs on its back, which have three distinct color bands. It is the smallest bat species in the eastern and midwestern US, with individuals weighing only 4.6–7.9 g (0.16–0.28 oz). This species mates in the fall before hibernation, though due to sperm storage, females do not become pregnant until the spring. Young are born helpless, though rapidly develop, flying and foraging for themselves by four weeks old. It has a relatively long lifespan, and can live nearly fifteen years.

White-nose syndrome (WNS) is a fungal disease in North American bats which has resulted in the dramatic decrease of the bat population in the United States and Canada, reportedly killing millions as of 2018. The condition is named for a distinctive fungal growth around the muzzles and on the wings of hibernating bats. It was first identified from a February 2006 photo taken in a cave located in Schoharie County, New York. The syndrome has rapidly spread since then. In early 2018, it was identified in 33 U.S. states and seven Canadian provinces; plus the fungus, albeit sans syndrome, had been found in three additional states. Most cases are in the eastern half of both countries, but in March 2016, it was confirmed in a little brown bat in Washington state. In 2019, evidence of the fungus was detected in California for the first time, although no affected bats were found.