Acoustic parameters related to behavioral discrimination of emotional vocalizations in Java Sparrows

Animals emit vocalizations related to internal or external states, such as hormone levels or predation risks. The Java Sparrow Lonchura oryzivora, a songbird, produces similar trill-structured calls in both aggressive and affiliative situations. A previous study found that trills produced in aggressive situations (AG trills) are faster, louder, and have a wider range of frequencies than trills produced in affiliative situations (AF trills). To assess whether Java Sparrows perceive these trills as different calls, we conducted a playback experiment using a habituation-dishabituation paradigm. In this paradigm, we first played a stimulus set for ten minutes (habituation stimulus), and after that we played either a test stimulus set or a control stimulus set. We analyzed behavioral changes in the study bird that took place between the last minute of the habituation stimulus and the next stimulus set (test or control). As trill stimuli, we used natural AG and AF trills (Experiment 1) and trills in which the trill rates and syllables types were modified (Experiment 2). The results showed that Java Sparrows distinguish between AG and AF trills (Experiment 1). However, when the trill acoustic structure was modified, they distinguished between the different syllable types, but not between different trill rates. As we used a natural behavior as an index, we could not measure the perceptual limit of trill discrimination in these birds. Instead, here, we asked whether the difference between AG and AF trills is meaningful or not, and which acoustic features were important for discrimination. To fully understand how birds perceive vocalizations in the context of communication, more experiments are required, both controlled experiments utilizing operant conditioning and electrophysiology, and multimodal experiments that reflect natural social relationships.