Bird calls are the short chips, caws and peeps that both male and female birds make all year. Compared to their unique and beautiful songs, calls are usually short, simple and unmelodic. But calls convey great meaning and birds use them to send up an alarm, keep in contact with each other, stay together during flight, and beg parents for food. Humans have tried to decode and categorize calls by grouping them based on their sounds, the situations in which they are used, and how other animals respond. But the question remains: Is that how the birds themselves categorize and understand them?
Working with Zebra Finches — gregarious songbirds that use around 11 distinct call types for social interactions — researchers ran auditory discrimination tasks* and found the birds both discriminate and categorize every call type in their repertoire. The telling detail was in the errors. When the birds got it wrong, they confused calls used in similar behavioral contexts more often than acoustic similarity alone would predict. In other words, a bird mixing up two sounds was confusing two ideas, not two audio waveforms. The authors conclude that Zebra Finches organize their calls into categories and hold a mental representation of what those sounds mean.