Transitive foraging behaviour in frog-eating bats

Most models of animal foraging assume that individuals make decisions rationally. One expectation of rationality theory is that preferences should be hierarchical or transitive. For many animals, including humans, making decisions about what to eat can become difficult when various parameters of choices are not positively related to one another and no single option may be considered the best. These complex decisions can result in irrational behaviour, suggesting that the value of any particular option may vary depending on the other available options. Here, we tested whether frog-eating bats, Trachops cirrhosus , are transitive in their preferences for frog calls. These bats attend to several attributes of the calls, such as call amplitude and complexity, when choosing a frog to target in their attack. While acoustic preferences are largely understood in isolation, we have a limited understanding of how bats choose between calls that vary along several important acoustic dimensions. Here, we conducted a series of binary choice experiments manipulating amplitude and complexity both separately and together to evaluate whether these bats make transitive foraging decisions. We found that bats are transitive in their rankings of calls based on these acoustic dimensions, with preferences reflecting a trade-off between both amplitude and complexity. Overall, our results add support to the notion that bats' preferences obey the general principles of rational behaviour and support the use of optimality approaches to the study of animal behaviour and decision making.