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Corynorhinus rafinesquii (Lesson, 1827)
Rafinesque's Big-eared Bat
Federal Protection: No US federal protection
State Protection: Rare
Global Rank: G3G4
State Rank: S3
Element Locations Tracked in Biotics: Yes
SWAP High Priority Species (SGCN): Yes
Element Occurrences (EOs) in Georgia: 47
Habitat Summary for element in Georgia: Pine forests; hardwood forests; caves; abandoned buildings; bridges; bottomland hardwood forests and cypress-gum swamps
The dorsal hair of Rafinesque's big-eared bat is brownish-gray in appearance. Individual hairs are dark brown to blackish at the base and pale reddish to brownish at the tips. The belly fur is dark at the base, contrasting sharply to whitish tips. Hairs on the feet project noticeably beyond the toes. The ears are very large, usually exceeding 30 mm (1¼ inches) in length, are joined at the base, and are curled similar to the horns of a ram when the bat is roosting. There are two distinctive side-by-side humps on the snout. The total length is 85 - 105 mm (3⅜ - 4 inches), the forearm length is 38 - 45 mm (1½ - 1⅞ inches), the wing spread is 26 - 30 cm (10 - 12 inches), and the weight is 8 - 13 grams (¼ - ½ ounce). There is an accessory cusp on the upper incisor, and females are somewhat heavier than males.
Townsend’s big-eared bat (Corynorhinus townsendii) does not occur in Georgia but is similar, particularly in that it also has very large ears. However, the belly fur of Townsend’s big-eared bat has buff tips that do not contrast sharply with the dark color of the base, the hairs on the feet do not extend beyond the toes, and the upper incisors lack the accessory cusp.
Rafinesque's big-eared bats are typically found in forested habitats. Roosting sites are usually in or near areas of mature forest, including bottomland and upland hardwoods and pine flatwoods with water nearby. Roosting sites are usually dimly lit sheltered areas, such as dilapidated buildings, bridges, hollow trees, loose bark, rock shelters, and the entrance zones of caves and mines. In coastal plain bottomland areas, Rafinesque’s big-eared bats utilize large, hollow cypress and gum trees with high basal area, openings near the base, and high canopy closure. Open canopies are unsuitable, as individuals are more vulnerable to predation.
Bats in the genus Corynorhinus have morphological adaptations that allow them to use gleaning and aerial-hawking foraging strategies to capture nocturnal flying insects. The diet of Corynorhinus, which includes Rafinesque’s big-eared bat, consists mostly of moths and butterflies. In Gregory et al.’s 2014 study, order Lepidoptera (moths and butterflies) represented 93.7% of the total volume of diet samples and was the only order to be observed in 100% of the samples. Orders Coleopterans (beetles), Hemiptera (true bugs), Diptera (true flies) and Hymenoptera (ants) were also represented.
While Rafinesque’s big-eared bats consistently consume larger moths and butterflies (macrolepidoptera) than smaller ones (microlepidoptera), recent studies have revealed that Corynorhinus bats consume a wider range of sizes and species of Lepidoptera than previously reported.
This species is perhaps the least known of any southeastern U.S. bat. In late fall, they gather in small groups to mate, then hibernate, in caves, rock shelters, mines, and similar structures with relatively stable winter temperatures. When the bat is roosting, its large ears are coiled alongside the head. In the spring, females form small maternity colonies of up to 100 individuals in relatively well lighted sites, typically in old buildings and rarely in caves and mines, to bear their single young in late May to early June. The young can fly at 3 weeks of age and are fully grown at 4 weeks. The males are solitary or form small groups during the summer, usually roosting in buildings and hollow trees away from the maternity colonies. They emerge to forage well after dark, so they are rarely observed or collected during periods of activity. They are known to live at least 10 years.
This species can be difficult to capture using standard mist nest sets. Roost sites can be located by searching potentially suitable locations, including hollow trees with basal openings, outbuildings, dilapidated structures, bridges, etc.
Although identifying bat calls to the species level can be difficult, acoustic surveys are a useful tool for surveying bats. These surveys are non-invasive, require fewer personnel, are less costly, and can be used to more readily survey multiple habitats when compared to direct capture of bats. Acoustic detections of bats can be used to get information on their range distribution, community structure, relative population size, temporal activity, and habitat use.
This secretive bat ranges widely throughout the southeastern U.S. but is abundant nowhere. It possibly occurs statewide throughout the year, but records from the Piedmont are lacking.
Bats are long-lived animals with low fecundity rates, making them more susceptible to environmental change. Consequently, bats are among the most threatened taxonomic groups worldwide. Requiring multiple, complex habitats, Rafinesque’s big-eared bats are threatened by habitat loss and degradation. Given their habitat requirements, Rafinesque’s big-eared bats are negatively impacted by the removal of large hollow trees or by reduced basal area and canopy closure associated with post-harvest forest structure. Declines are probably also due to pesticides.
Apparent rarity might be the result of few observations or collections of foraging bats due to their highly nocturnal nature. Recent surveys revealed many more locations than had previously been reported and extended the known range into the upper coastal plain. Unlike most bats, which become active well before dark, big-eared bats do not emerge from their roost until complete darkness has arrived. They are easily disturbed and are quick to arouse and take flight when discovered on the roost.
Pseudogymnoascus destructans the causal agent of white-nose syndrome (WNS), has led to widespread mortality of hibernating bats across the eastern North America. During the winters of 2012-2013 and 2013-2014, Bernard et al. took skin swabs from eight Rafinesque’s big-eared bats in Tennessee. This resulted in the first confirmed record of WNS on Rafinesque’s big-eared bat, though no mortality from WNS has been observed in this species. WNS is a fungal pathogen that targets hibernating bats. Understanding torpor behavior may be important in identifying different species’ susceptibilities to WNS. Jackson et al. radio and PIT tagged Rafinesque’s big-eared bats in 2010 and monitored their torpor behavior for the following 2 winters. Their results indicated that Rafinesque’s big-eared bat is a comparatively shallow hibernator and is relatively active during the winter. Therefore, it is hypothesized that the species has an ecological and physiological buffer against P. destructans, and that the species may be better suited to withstand fungal infection when compared to other cave-hibernating bats in eastern North America.
Rafinesque’s big-eared bat is labeled as “Rare” in Georgia, but currently has no federal protections. A species of concern, Rafinesque’s big-eared bat populations continue to be impacted by the elimination of mature forest habitats, particularly coastal plain river bottom forests. With many other bat species, it is difficult to estimate population abundance, and this remains the primary obstacle in proactive conservation management of species. Recent additional survey efforts done by Clement and Castleberry indicate that this species is more abundant than had been previously estimated. Continued survey efforts and discovery of new populations could increase population abundance estimates.
Additional areas of occupied habitat need to be identified through surveys. Silvicultural practices to alter the structure of forest habitat for the benefit of wildlife can improve the quality of habitat for generalist and forest-interior bats. These practices provide heterogenous forest structure that includes dead wood and high basal area of large trees. Higher basal area was associated with higher detection of Rafinesque’s big-eared bats. Implementation of artificial roosting sites where natural ones are scarce could also improve populations.
Clement and Castleberry’s predictive population models indicate that semi-permanently flooded wetland was 20 times as likely as saturated wetland to provide appropriate roosting habitat. Additionally, colony abundance was most affected by wetland width, with narrow wetlands being significantly preferred to wider areas. Modifications that improve forest hydrology will also benefit the species.
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Jordan, J. R. 1986. Rafinesque's big-eared bat, Plecotus rafinesquii Lesson. Pages 112-113 in R. H. Mount (ed.). Vertebrate Animals of Alabama in Need of Special Attention. Alabama Agricultural Experiment Station, Auburn University, Auburn.
Menzel, M. A., B. R. Chapman, W. M. Ford, J. M. Menzel, and J. Laerm. 2000. A review of the distribution and roosting ecology of bats in Georgia. Georgia Journal of Science 59: 143-178.
Trani, M. K., W. M. Ford, and B. R. Chapman. 2007. The land manager’s guide to mammals of the South. The Nature Conservancy, Durham, North Carolina. 566 pp.
Whitaker, J. O., Jr., and W. J. Hamilton, Jr. 1998. Mammals of the eastern United States. Cornell University Press, Ithaca, New York. 583 pp.
Jim Ozier
J. Ozier, Aug. 2008: original account
K. Owers, Sept. 2009: updated status and ranks, added picture
S. Krueger: updated account and reviewed for final
