Our newest postdoctoral researcher May Dixon and her co-authors (Patty Jones, Mike Ryan, me, and Rachel Page) have a new paper entitled “Long-term memory in frog-eating bats” in the journal Current Biology. The frog-eating bat (or fringe-lipped bat) is an acoustic eavesdropping predator that learns and remembers the calls of different frogs and katydids. As a PhD student, Patty Jones (now a professor at Bowdoin College) had trained several frog-eating bats (Trachops cirrhosus) to respond to a novel sound by flying towards it to receive a food reward. Years later, May Dixon, during her PhD, re-captured and re-tested the memory of 8 of these bats that Patty had previously trained in captivity up to 4 years ago.
May found that all the trained bats remembered the sound they learned in captivity. She confirmed this by comparing their responses to a naive control group, which had much lower responses to the sounds. We don’t know if the frog-eating bat’s memory is especially good for a mammal or a bat (nobody really knows much about duration of bat memory), but we might expect frog-eating bats to have a pretty good memory for sounds because they learn the calls of multiple prey species (including frogs and katydids) to tell them apart from unpalatable species. Some of these prey need to be remembered for a while because they are encountered only sporadically or seasonally.
Such demonstrations of long-term memory in wild animals are rare but important. Most data on memory in nonhuman animals comes from captive animals that have grown up in simplistic impoverished environments that don’t place the same cognitive demands on animals as the vast and complex natural world. The hippocampus, an area of brain involved in spatial memory, is almost 25% smaller in captive black-capped chickadees compared to their counterparts in the wild (Tarr et al. 2009 Developmental Neurobiology).
Although never published, May and I also did a very simple memory test with one vampire bat that we re-captured in 2019 after being in captivity in 2016-2017. We placed several wild caught bats in small cages with blood feeders. Bats that had never been in captivity did not approach the feeders, not knowing what they were, but this previously captive bat immediately jumped down and fed from it, suggesting that it also remembered what it learned in captivity over 2 years ago. It would not surprise me at all if bats could remember salient associations for many years. I would love to test the social cognitive skills of vampire bats.