Long-term memory in frog-eating bats.

Long-term memory has clear advantages for animals but also has neurological and behavioral costs1-3. Encoding memories is metabolically expensive1. Older memories can interfere with retrieval of more recent memories3, prolong decision-making and reduce cognitive flexibility2,3. 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.

Hearing sensitivity: An underlying mechanism for niche differentiation in gleaning bats.

Tropical ecosystems are known for high species diversity. Adaptations permitting niche differentiation enable species to coexist. Historically, research focused primarily on morphological and behavioral adaptations for foraging, roosting, and other basic ecological factors. Another important factor, however, is differences in sensory capabilities. So far, studies mainly have focused on the output of behavioral strategies of predators and their prey preference. Understanding the coexistence of different foraging strategies, however, requires understanding underlying cognitive and neural mechanisms. In this study, we investigate hearing in bats and how it shapes bat species coexistence. We present the hearing thresholds and echolocation calls of 12 different gleaning bats from the ecologically diverse Phyllostomid family. We measured their auditory brainstem responses to assess their hearing sensitivity. The audiograms of these species had similar overall shapes but differed substantially for frequencies below 9 kHz and in the frequency range of their echolocation calls. Our results suggest that differences among bats in hearing abilities contribute to the diversity in foraging strategies of gleaning bats. We argue that differences in auditory sensitivity could be important mechanisms shaping diversity in sensory niches and coexistence of species.