Rationality in decision-making in the fringe-lipped bat, Trachops cirrhosus

Most models of animal behavior assume rationality in animal's decisions, with animals maintaining strict preferences for different options (e.g., optimal foraging theory). In the wild, however, animals often choose among several options simultaneously, and their evaluation of each prey type may depend on the perceived relative values of other choices. Fringe-lipped bats (Trachops cirrhosus) are promising subjects for studying how animals make decisions. When given a choice between the calls of two species of frogs, T.cirrhosus will choose the more salient call that is associated with the higher capture rate. Although in the wild T.cirrhosus often choose among multiple call options, most tests of prey preferences in this system include only two options. In this experiment, we tested whether T.cirrhosus alters relative preference for two call types that differ along two acoustic dimensions (amplitude and complexity) when presented with a third, "decoy" option, inferior to the two original options along either one or both dimensions. Results from this study demonstrate that under these circumstances, T.cirrhosus evaluates all three options independently of one another, and thus, preferences remain consistent and rational in both the presence and absence of a decoy. These results counter many other experiments suggesting irrationality in animal decision-making. Significance statement A fundamental assumption of animal behavior is that animals make rational decisions. However, most animals are tested in ways that rely on simple binary choice experiments. Because animals are often faced with multiple options simultaneously in the wild, these tests may often fail to capture the complexity necessary to understand cognitive limitations that naturally influence animal decisions. In certain cases, complex decisions can result in irrational behavior that is inconsistent with what is found in binary choice studies. Here, we conducted a test with fringe-lipped bats to determine whether their choices for specific frog calls were influenced by the number of options in a choice set. We found that, unlike many other animals, the fringe-lipped bats appear to make consistent decisions, even with more complex choice sets. Our results indicate that there are likely to be strong selective pressures on rational decision-making in this species, perhaps shaped by high metabolic requirements.