The evening bat (Nycticeius humeralis) is a species of bat in the vesper bat family that is native to North America.[2] Hunting at night, they eat beetles, moths, and other flying insects.
The evening bat is a small bat weighing 7–15 g (0.25–0.53 oz)[3] found throughout much of the midwestern and eastern United States. Their forearms are 34–38 mm (1.3–1.5 in) in length.[4] 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.[4] They have wide, dog-like muzzles, pronounced facial glands, and disproportionately large bacula.[4][5] 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.[6] They have an unkeeled calcar and a short, round tragus.[7] The curvature of the tragus helps distinguish it from bats of the genus Myotis, which otherwise look very similar.[7] Their skull has one upper incisor on each side with 4 molariform teeth.[8]
The evening bat is a relatively short-lived, especially compared to other bats in its geographic range.[9] It has a maximum age of 6 years, though few individuals live past 4 years.[10][9] 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.[9]
Evening bats mate in the fall and winter; the sperm is stored until the spring, when fertilization occurs.[11] Female bats form maternity colonies in May,[12] consisting of 15-300 individuals.[3] Of females that give birth, 90% have twins, but singletons and triplets are also possible.[11][12][13] Though it is more common for evening bats to nurse their own offspring,[3] a small proportion of offspring are nursed by unrelated females. The pups are capable of flight within a month of birth.[12] Pups are weaned within 42 days of birth.[3] Female pups exhibit natal philopatry, meaning that as adults, they return to the roost where they were born to give birth.[3]
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.[14] In southern Illinois, the spotted cucumber beetle is almost 25% of the evening bats' diet.[15] Other beetles consumed include ground beetles and scarab beetles.[14] Moths are also a significant dietary component.[14] Bugs, winged ants, and flies are prey items of less significance.[15][16] Evening bats partition resources with other insectivorous bats in their range, such as the eastern red bat and Seminole bat.[16] Despite foraging in the same areas at the same time, these three bat species choose different prey items at different points throughout the summer.[16]
At first, the evening bat was thought of as a southeastern bat species.[17] However, breeding evening bats have been found as far north as Michigan and as far west as the 100th meridian.[13] Evening bats roost in a variety of structures, including Spanish moss, under bark, in tree cavities, and in buildings.[18] For foraging habitat, evening bats in Georgia prefer pine forest, riparian zones, and open fields.[19] Evening bats have home ranges of approximately 300 hectare (1.15 mi2).[19] 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.[4]
While the evening bat is considered endangered in the state of Indiana,[20] it has a cosmopolitan distribution throughout the southeast and midwest.[18] 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.[21] 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.[21][22]
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.
