Long-term memory in frog-eating bats

Long-term memory has clear advantages for animals but also has neurological and behavioral costs^1-3. Encoding memories is metabolically expensive¹. Older memories can interfere with retrieval of more recent memories³, prolong decision-making and reduce cognitive flexibility^2,3. Given these opposing selection pressures, understanding how long memories last can shed light on how memory enhances or constrains animals' abilities to exploit their niches. Although testing memory retention in wild animals is difficult, it is important because captive conditions do not reflect the complex cognitive demands of wild environments, and long-term captivity changes the brain⁴ (Data S1A). Here, we trained wild-caught frog-eating bats (Trachops cirrhosus) to find prey by flying to a novel acoustic cue. After they learned the rewarded sound, we released them back into the wild, and then re-captured some of them one to four years later. When re-tested, all eight 'experienced' bats that previously learned the novel prey sounds flew to those sounds within seconds, whereas 17 naïve bats tested with the same sounds showed weak responses. Experienced bats also showed behavior indicating generalization of memories between novel sounds and rewards over time. The frog-eating bat's remarkably long memory indicates that an ability to remember rarely encountered prey may be advantageous for this predator and suggests hitherto unknown cognitive abilities in bats.