Short answer
Appears to be an evening bat (Nycticeius humeralis) or little brown bat (Myotis lucifugus).
Long answer.
You can see a list of common bat species in Georgia through the Georgia Department of Natural Resources. (A high-res image of a visual poster can be seen here).
According to Greenhall and Frantz (1994)1, three of the species found in Georgia are among the species most found in and around buildings: big brown bat (Eptesicus fuscus), evening bat (Nycticeius humeralis), and little brown bat (Myotis lucifugus)
Your image is relatively good, but it does not provide enough detail of key structures to definitively say which species it is. (see Morgan et al. (2019)2 for a key).
If we go simply based on size, the evening bat seems to be closest to your specimen:
- E. fuscus is typically 4.1-5.1 inches in length (source), which is larger than your specimen
- Your specimen is larger than a typical M lucifugus (1.8-2.3 inches, source).
- N. humeralis is more similarly sized (average is 3.4 inches, source).
It appears that your bat has a broad nose, which would hint toward big brown bat (Eptesicus fuscus) or an evening bat (Nycticeius humeralis).
According to GeorgiaBiodiversity.com:
The evening bat is commonly confused with the big brown bat due to its fur color and broad muzzle. However, the evening bat is much smaller and does not have a keeled calcar. The evening bat's rounded tragus distinguishes it from all other small bats except the eastern pipistrelle, which has tri-colored rather than bicolored dorsal fur. The evening bat also has just two upper incisors instead of the four typical of all myotis.
Wait, keeled calcar? Huh?
- A calcar is the spur of cartilage coming off the lateral side of the ankle of bats. The image below roughly dmeonstrates the difference between keeled and not keeled.
Left is keeled; Right is not keeled. Source: Fig 12, Morgan et al. (2019)2
Your specimen does not appear to have a keeled calcar, which would suggest further that this is more likely an evening bat versus a big brown bat.
However, the little brown bat also lacks a keeled calcar....
Though many sources do not directly compare the little brown and evening bat, Morgan et al.'s (2019) key splits these species at the same step, suggesting they have much in common. Morgan et al.'s differentiating characteristics for these species include:
Hair on hind foot extends beyond tips of claws; tragus long and blunt; underwing lightly furred to elbow: Myotis lucifugus (Little Brown Bat).
No long hair on foot; tragus is short, blunt and curved; underwing, muzzle, and uropatagium are hairless: Nycticeius humeralis (Evening Bat)
According to Greenhall and Frantz (1994)1,
[the evening bat] bears some resemblance to the somewhat smaller little brown bat (M. lucifugus) but can be identified by its characteristic blunt tragus.
To reiterate, the "sharply-pointed" tragus (source) of M. lucifigus and the presence of long toe hairs extending beyond the length of the toe claws (source) would both definitively point toward the little brown bat vs the evening bat. However, neither characteristics is really distinguishable in your photograph.
As such, I don't feel fully confident to rule one out over the other.
It's 3 am though, so perhaps I should stare at your image more in the morning after some rest...I'll update further if I notice anything definitive.
1. Greenhall, A.M. and Frantz, S.C., 1994. Bats (Myotis lucifugus). The Handbook: Prevention and Control of Wildlife Damage, p.46.
2. Morgan, C.N., Ammerman, L.K., Demere, K.D., Doty, J.B., Nakazawa, Y.J. and Mauldin, M.R., 2019. Field identification key and guide for bats of the United States of America. Occasional papers (Texas Tech University. Museum), 360.
