Art Credit: Sahina Irvin
Appearance
The hoary bat is the second largest species of bat in Florida. It weighs anywhere between 20 and 35 grams (about the weight of one silver dollar) and has a wingspan of about 15 inches (Marks and Marks 2006). This species has unique fur color that ranges from dark brown to cream, with white tips. These white tips give the bat a frosted appearance and serve as the inspiration for its name. Hoary comes from a type of frost sometimes found on plants called hoarfrost. The hoary bat has fur on its tail and feet, and short, rounded ears (Marks and Marks 2006). The combination of its hairy tail and the frosted or ashy-looking fur gives its Latin name: Lasiurus (“hairy tailed”) cinereus (“ashen”). In this species, males can be one and a half times larger than females (Shump and Shump 1982).
Behavior
Like all Florida bats, the hoary bat is insectivorous, meaning they eat primarily insects. Because they are so large, hoary bats tend to feed on larger insects. They prefer moths but will also eat beetles, mosquitoes, wasps, and other flying insects (Marks and Marks 2006). This species normally emerges later in the evening than most other species of bats and flies directly to their hunting grounds or a water source (Marks and Marks 2006). They are fast flyers, known to reach speeds of up to 17mph (Cueva Salcedo et al. 1995). Like most bats, hoary bats use echolocation to find their prey. By frequently emitting high-pitched calls and listening to the echo, they can home in on an insect’s exact location as they fly by. However, unlike most other bats, hoary bats will often avoid using echolocation to navigate and avoid obstacles in flight. This may be to prevent attracting other, competing hoary bats to food sources, and may help explain why they seem to be so susceptible to windmill strikes (Corcoran and Weller 2018).
Little is known about the reproductive cycle and mating habits of the hoary bat because the species is both solitary and migratory (Koehler and Barclay 2000). Females with young pups are found throughout the northern half of its range in the summer, as far south as Georgia. No females with pups have been found in Florida (Marks and Marks 2006). They give birth to twin pups from mid-May through early July (Koehler and Barclay 2000, Marks and Marks 2006). Because they roost in trees, the pups are more exposed to the elements than the pups of other bat species that roost in caves or other sheltered locations, with weaning occurring after 7 weeks (Koehler and Barclay 2000).
Habitat
The hoary bat is a tree-dwelling species. They prefer to roost alone, typically in tree leaves, but occasionally in tree cavities, where their frosted appearance is an effective camouflage against the tree bark (Marks and Marks 2006). When they roost, they like to be concealed from all sides except below, so they can drop down into flight when they leave at night to look for food. They will roost in both pine and hardwood forests, typically in trees on the edge of clearings and meadows (Constantine 1966, Gruver 2002, Perry and Hill 2007). The hoary bat is migratory, moving to warmer climates in the winter (Cryan and Wolf 2003). In Florida, they are only found in the winter, between the months of October and April, before migrating back north for the summer (Zinn and Baker 1979).
Threats
One of the biggest threats to hoary bats is the spread of wind turbines. These structures kill over 500,000 bats across the U.S. and Canada each year, with hoary bats making up the majority of these deaths (Frick et al. 2017). The combination of their migratory nature with how they avoid using echolocation to navigate may make these bats particularly susceptible to collision with wind turbines (Corcoran and Weller 2018). However, it may be that they are attracted to tall structures for social or other reasons (Jameson and Willis 2014). Regardless of why these collisions happen, it’s estimated that the general population of hoary bats could decline by as much as 90% by 2070 as a result (Frick et al. 2017).
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 record the calls of nearby bats. In addition, the 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
Constantine, D. G. (1966). Ecological observations on lasiurine bats in Iowa. Journal of Mammalogy, 47(1), 34-41.
Corcoran, A. J., & Weller, T. J. (2018). Inconspicuous echolocation in hoary bats (Lasiurus cinereus). Proceedings of the Royal Society B: Biological Sciences, 285(1878), 20180441.
Cryan, P. M. & Wolf, B. O. (2003). Sex differences in the thermoregulation and evaporative water loss of a heterothermic bat, Lasiurus cinereus, during its spring migration. Journal of Experimental Biology. 206 (19): 3381–3390.
Cueva Salcedo, H. D. L., Fenton, M. B., Hickey, M. B. C., & Blake, R. W. (1995). Energetic consequences of flight speeds of foraging red and hoary bats (Lasiurus borealis and Lasiurus cinereus; Chiroptera: Vespertilionidae). Journal of Experimental Biology, 198(11), 2245-2251.
Frick, W. F., Baerwald, E. F., Pollock, J. F., Barclay, R. M., Szymanski, J. A., Weller, T. J., ... & McGuire, L. P. (2017). Fatalities at wind turbines may threaten population viability of a migratory bat. Biological Conservation, 209, 172-177.
Gruver, J. C. (2002). Assessment of bat community structure and roosting habitat preferences for the hoary bat (Lasiurus cinereus) near Foote Creek Rim, Wyoming. University of Wyoming.
Jameson, J. W. & Willis, C. K. R. 2014. Activity of tree bats at anthropogenic tall structures: implications for mortality of bats at wind turbines. Animal Behaviour. 97: 145–152.
Koehler, C. E., & Barclay, R. M. (2000). Post-natal growth and breeding biology of the hoary bat (Lasiurus cinereus). Journal of Mammalogy, 81(1), 234-244.
Marks, C. S. & Marks, G. E. (2006) Bats of Florida. University Press of Florida. Gainesville, Fl. 176 pp.
Perry, R. W., & Thill, R. E. (2007). Roost characteristics of hoary bats in Arkansas. The American Midland Naturalist, 158(1), 132-138.
Shump, Jr., K. A.& Shump, A. U. (1982). Lasiurus cinereus. Mammalian Species. 85 (185): 1–5.