The evening bat (Nycticeius humeralis) is a species of bat in the vesper bat family that is native to North America. Hunting at night, they eat beetles, moths, and other flying insects.
The evening bat is a small bat weighing found throughout much of the midwestern and eastern United States. Their forearms are in length. The tip of each dorsal hair is a light gray, and one to two-thirds of the basal is dark brown. Though there have been some cases of white pelage, the majority of the population is mostly brown in color.[1] They have wide, dog-like muzzles, pronounced facial glands, and disproportionately large bacula.[1] [2] Evening bats can be mistaken for juvenile big brown bats, due to their physical resemblance but smaller size.
Evening bats have relatively robust jaws, compared to other insectivorous bats.[3] They have an unkeeled calcar and a short, round tragus.[4] The curvature of the tragus helps distinguish it from bats of the genus Myotis, which otherwise look very similar.[4] Their skull has one upper incisor on each side with 4 molariform teeth.[5]
The evening bat is a relatively short-lived, especially compared to other bats in its geographic range.[6] It has a maximum age of 6 years, though few individuals live past 4 years.[7] [6] Its short lifespan for a bat could be explained by its considerably higher reproductive output. Bats that only have one pup per year would need to live much longer to have the same fitness as a shorter-lived species with two or three pups per year.[6]
Evening bats mate in the fall and winter; the sperm is stored until the spring, when fertilization occurs.[8] Female bats form maternity colonies in May,[9] consisting of 15-300 individuals. Of females that give birth, 90% have twins, but singletons and triplets are also possible.[8] [9] [10] Though it is more common for evening bats to nurse their own offspring,[11] a small proportion of offspring are nursed by unrelated females. The pups are capable of flight within a month of birth.[9] Pups are weaned within 42 days of birth.[11] Female pups exhibit natal philopatry, meaning that as adults, they return to the roost where they were born to give birth.[11]
These bats have varied diets. A majority of the bats' diet in Indiana and Illinois are beetles, including the spotted cucumber beetle, which is a serious agricultural pest.[12] In southern Illinois, the spotted cucumber beetle is almost 25% of the evening bats' diet.[13] Other beetles consumed include ground beetles and scarab beetles.[12] Moths are also a significant dietary component.[12] Bugs, winged ants, and flies are prey items of less significance.[13] Evening bats partition resources with other insectivorous bats in their range, such as the eastern red bat and Seminole bat.[14] Despite foraging in the same areas at the same time, these three bat species choose different prey items at different points throughout the summer.[14]
At first, the evening bat was thought of as a southeastern bat species.[15] However, breeding evening bats have been found as far north as Michigan and as far west as the 100th meridian.[10] Evening bats roost in a variety of structures, including Spanish moss, under bark, in tree cavities, and in buildings.[16] For foraging habitat, evening bats in Georgia prefer pine forest, riparian zones, and open fields.[17] Evening bats have home ranges of approximately 300 hectare (1.15 mi2).[17] Because the evening bat is not found in the northernmost extent of its range in the winter, it is likely that at least some evening bats are migratory.[1]
While the evening bat is considered endangered in the state of Indiana,[18] it has a cosmopolitan distribution throughout the southeast and midwest.[16] Because evening bats do not enter or hibernate in caves, the species is not at-risk from white-nose syndrome, which has killed over six million bats in the United States since 2006.[19] The evening bat's avoidance of this disease, along with die-offs of many other species, is possibly responsible for the evening bat recently expanding its range into Wisconsin in 2015 and Minnesota in 2016.[19] [20]
| State | Conservation Status | |
|---|---|---|
| Alabama | Lowest Conservation Concern | |
| Arkansas | Not listed | |
| Florida | Not listed | |
| Georgia | Not listed | |
| Illinois | Not listed | |
| Indiana | State Endangered | |
| Iowa | Not listed | |
| Kentucky | Threatened | |
| Kansas | Not listed | |
| Louisiana | Not listed | |
| Maryland | Not listed | |
| Michigan | Threatened | |
| Minnesota | Not listed | |
| Mississippi | Not listed | |
| Missouri | Not listed | |
| Nebraska | Not listed | |
| North Carolina | Not listed | |
| Ohio | Species of Special Interest | |
| Oklahoma | Not listed | |
| Pennsylvania | Not listed | |
| South Carolina | Not listed | |
| Tennessee | Not listed | |
| Texas | Not listed | |
| Virginia | Not listed | |
| West Virginia | Not listed | |
| Wisconsin | Not listed |