Big brown bat

The big brown bat (Eptesicus fuscus) is a species of vesper bat distributed widely throughout North America, the Caribbean, and the northern portion of South America. It was first described as a species in 1796. Compared to other microbats, the big brown bat is relatively large, weighing 15–26 g (0.53–0.92 oz) and possessing a wingspan of 32.5–35 cm (12.8–13.8 in).

Big brown bats are insectivorous, consuming a diverse array of insects, particularly night-flying insects, but especially beetles. Some of the beetles it consumes are serious agricultural pests, including cucumber beetles. They are nocturnal, foraging for prey at night and roosting in sheltered areas during the day such as caves, tunnels, tree cavities, and human structures. Their breeding season is in the fall, shortly before their annual hibernation. After hibernation ends in the spring, females form maternity colonies for giving birth to young. Oftentimes only one offspring is produced per litter, though twins are common in the Eastern US. Lifespans of 6.5 years are considered average.

The big brown bat occurs widely throughout the US, Canada, Central America, and the Caribbean. Its range extends into parts of South America, found as far south as Colombia and Venezuela. It is adaptable to many habitats and is considered a generalist species. The big brown bat is not considered at risk for extinction, and is evaluated as the lowest conservation priority by the International Union for Conservation of Nature (IUCN).

While some other bat species in its range have experienced dramatic population declines due to the fungal disease white-nose syndrome, the big brown bat is relatively resistant to the effects of the disease, and some populations have even increased since the syndrome arrived in North America. Like all bats in the US, the big brown bat can be impacted by rabies, though some individuals have immunity against the virus. Even though sick bats are more likely to be submitted for testing, in 2011, only 3.8% of submitted big brown bats were positive for the rabies virus. Bat boxes are sometimes used to attract them as they are an agriculturally valuable species.

The big brown bat was described in 1796 by French naturalist Palisot de Beauvois. Palisot described the species based on specimens in the Philadelphia Museum of Charles Willson Peale, an American naturalist, giving it the name Vespertila fuscus. The genus name, Eptesicus, is likely derived from the Greek words ptetikos ("able to fly") or petomai ("house flier"), and the species name "fuscus" is Latin in origin, meaning "brown". The big brown bat is the type species for the genus Eptesicus, which was established in 1820 by French-American naturalist Constantine Samuel Rafinesque. Though Rafinesque designated the type species as Eptesicus melanops, this was later determined to be a synonym of Eptesicus fuscus. The first use of the current name combination Eptesicus fuscus was in 1900 by Hungarian zoologist Lajos Méhelÿ. Recognized subspecies number eleven or twelve:

E. f. lynni has sometimes been considered a full species, though was listed as a subspecies by the American Society of Mammalogists and the Integrated Taxonomic Information System (ITIS) as of 2019. In the US state of Colorado where two subspecies were hypothesized to overlap (E. f. fuscus and E. f. pallidus), morphological features did not agree with genetic lineages, and thus were not reliable in distinguishing the two subspecies. Individuals with eastern and western US genetic lineages co-occurred in the same colonies, however.

As the genus Eptesicus is fairly speciose, it is further divided into morphologically similar "species-groups". The big brown bat belongs to the serotinus group, which is defined by having a large, elongate skull, flat braincase, and a long snout. In a study of the evolutionary relationships of some Eptesicus species, the big brown bat was most closely related to the two other species from the Americas: the Argentine brown bat and the diminutive serotine. The serotinus group also includes:

It is a relatively large microbat, weighing 15–26 g (0.53–0.92 oz). Adult body length is 110–130 mm (4.3–5.1 in). Its forearm is usually longer than 48 mm (1.9 in). The tail is 47–52 millimetres (1.9–2.0 in) and the hind legs are 10 millimetres (0.39 in). Its wingspan is 32.5–35 cm (12.8–13.8 in). Its dorsal fur is reddish brown and glossy in appearance; its ventral fur is lighter brown. Its snout, uropatagium (flight membrane between the hind limbs), and wing membranes are black and hairless. Its ears (12–13 millimetres [0.47–0.51 in]) are also black; they are relatively short with rounded tips. The tragi (cartilage flaps in front of the ear canal) also have rounded tips.