Appearance
The evening bat is one of Florida’s smallest bats, with a wingspan of just 10-11 inches and a weight of 7-14 grams (approximately 1-2 quarters) (Marks and Marks 2006). They have brown fur on their back and yellow to tan fur on their stomach, with short brown ears, a broad, hairless muzzle, and dark brown, hairless wings (Watkins 1972). They can be easily mistaken for a juvenile big brown bat (Eptesicus fuscus), though the adult big brown bats are significantly larger.
Behavior
Like all Florida bats, the evening bat is insectivorous, meaning it eats insects. Specifically, the evening bat mostly hunts beetles and moths, but it will eat other flying insects when it can (Whitaker and Clem 1992). Many of these prey insects are serious agricultural pests including its most preferred prey, the spotted cucumber beetle. This beetle can cause widespread damage to cucumber, squash, and corn crops, which evening bats help prevent. Interestingly, the evening bat has shown that it can change its preferred diet to avoid competition with other bat species, a strategy scientists call “resource partitioning” (Carter et al. 2004).
Evening bats leave their roost to start hunting shortly after sunset, a behavior that gives them their name. They tend to be low and slow flyers, staying over open areas such as forest meadows and bodies of water (Nowak 1999). Like most bats, the species uses echolocation to find its prey. By frequently emitting high-pitched calls and listening to the echo, they can home in on an insect’s exact location (Simmons et al. 1996).
Evening bats mate in the late summer to early fall, but the female can delay the actual fertilization until spring. In May, they begin forming maternity colonies of 15-300 bats to raise their pups, which takes around 42 days (Wilkinson 1992). These pups are usually born as twins, but singletons and triplets are also possible (Watkins and Shump 1981). Outside of maternity season, evening bats still like to roost in large groups called colonies, often with several hundred bats. They will even roost with other bat species (Ober et al. 2004).
Evening bats migrate to warmer climates starting in the fall, though bats in Florida usually migrate much shorter distances given the state’s generally warm weather. They are a relatively short-lived species, with most wild bats only surviving 2 to 4 years (Austad 2010).
Habitat
Evening bats are found throughout Florida except for the Keys, and they can roost in many kinds of places. They tend to prefer natural roosts such as tree cavities, beneath tree bark, and in crevices, but will also happily roost in human structures such as underneath bridges, in attic spaces, in folded umbrellas, and in bat houses (Menzel et al. 2001). They do not roost in caves. They are often found flying over forest meadows and other open areas like rivers, ponds, and lakes (Kurta 2001).
Threats
Deforestation from increased human development is a major threat to evening bats. This species prefers to roost in heavily forested areas. As these areas are converted into human developments, evening bats are losing much of their roosting habitat. When they do lose their roosting trees, they tend to move into nearby human structures. This increases human-wildlife conflict to the detriment of both people and bats.
Conservation and Management
These bats are monitored with the other bat species in Florida as part of the Long-term Bat Monitoring Program, which seeks to keep track of bat populations throughout the state. The program achieves this by placing ultrasonic detectors across the state that pick up and record calls of nearby bats. In addition, FWC performs yearly surveys of caves to check for the fungus that causes white-nose syndrome.
It is illegal to remove bats from structures or to otherwise handle them directly in the state of Florida. If you have bats in your house or other structure, please see our Living With Bats page to learn how to properly evict them.
How You Can Help
We are always glad to have volunteer help with our bat conservation work, particularly with the Long-term Bat Monitoring Program in which volunteers help place and monitor our acoustic detectors. If you are interested in volunteering with this program or in helping in other ways, please visit our Bat Force website to learn more.
References
Austad, S. N. (2010). “Cats, ’rats,’ and bats: the comparative biology of aging in the 21st century.” Integrative and comparative biology, icq131.
Barbour, R., W. Davis. 1974. Mammals of Kentucky. Kentucky: The University Press of Kentucky.
Carter, T. C., Menzel, M. A., Chapman, B. R., & Miller, K. V. (2004). “Partitioning of food resources by syntopic eastern red (Lasiurus borealis), Seminole (L. seminolus) and evening (Nycticeius humeralis) bats.” The American Midland Naturalist, 151(1), 186-191.
Kurta, A. 2001. Mammals of the Great Lakes Region. Ann Arbor, Michigan: The University of Michigan Press.
Marks, C. S. and G. E. Marks. Bats of Florida. 2006. University Press of Florida. Gainesville, Fl. 176 pp.
Menzel, M. A., Carter, T. C., Ford, W. M., & Chapman, B. R. (2001). “Tree-roost characteristics of subadult and female adult evening bats (Nycticeius humeralis) in the Upper Coastal Plain of South Carolina.” The American Midland Naturalist, 145(1), 112-119.
Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: The Johns Hopkins University Press.
Ober, Holly K., Main, Martin B., Allen, Ginger M., 2004. Bats of Florida, Institute of Food and Agricultural Sciences. http://edis.ifas.ufl.edu/uw203
Simmons, J., M. Ferragamo, T. Haresign, J. Fritz. Aug 1996. “Representation of Perceptual Dimensions of Insect Prey During Terminal Pursuit by Echolocating Bats.” Biological Bulletin, 191:(1): 109-121.
Watkins, L. C. (1972). Nycticeius humeralis. Mammalian species, (23), 1-4.
Watkins, L. C., & Shump Jr, K. A. (1981). “Behavior of the evening bat Nycticeius humeralis at a nursery roost.” The American Midland Naturalist, 258-268.
Whitaker Jr, J. O., & Clem, P. (1992). “Food of the evening bat Nycticeius humeralis from Indiana.” The American Midland Naturalist, 211-214.
Wilkinson, G.S. (1992). "Communal Nursing in the Evening Bat, Nycticeius humeralis". Behavioral Ecology and Sociobiology. 31 (4): 225–235.