In experiments with black-capped chickadees native to North America, scientists were able to show that the songbirds attach great importance to the correct order of the individual notes in certain calls that are used to communicate with conspecifics. The researchers recently reported their findings in the journal Behavioral Processes.
“We found that in the so-called chick-a-dee calls of birds, used for example to warn of enemies, the order of the four notes used is always the same: note A comes before B, B comes before C and C comes before D. Individual notes can also be omitted or repeated, resulting in several hundred possible combinations that all follow the basic order,” explains co-author Marisa Hoeschele from the Acoustics Research Institute of the Austrian Academy of Sciences (OeAW).
Enemy warning
Black-capped chickadees can use this simple four-note grammar to send different messages to their conspecifics. “We know from another study, for example, that warnings about an owl repeat the D note very often at the end of the call, while less dangerous enemies do not trigger as many repetitions,” says Hoeschele.
With an ingenious experiment, the researchers were able to demonstrate that black-capped chickadees actually recognize incorrect sentence structure as a category. For this purpose, the birds were offered three different perches: one without noise, one with a loudspeaker that played chick-a-dee calls with the correct sequence of notes, and one on which calls with incorrect sentence structure were played. “We could see a clear preference for the correct calls. This shows that the birds do indeed have categories for right and wrong sequences of notes. We artificially generated the right and wrong sequences of notes so that possible preferences for natural calls did not skew the experiment,” Hoeschele says.
Complex animal languages?
In a second step, the researchers were also able to identify individual differences in the birds’ language ability. The black-capped chickadees were trained to identify incorrect sequences of notes with the help of rewards. It turned out that the individuals who showed a stronger preference for the correct sequence of notes in the first experiment also learned to signal the scientists more quickly when they heard incorrect calls. “Incorrect sequences of notes do not actually occur in black-capped chickadees; the birds naturally always follow the correct sequence. But some individuals seem to have a special gift for such language games,” Hoeschele says.
It is still unclear how complex the language of black-capped chickadees really is and what content can be communicated with it. “Besides the chick-a-dee calls, black-capped chickadees use a number of other calls, some of which are even more complicated and the rules of which we have not yet investigated. Likewise, other songbirds, parrots, whales, dolphins, and elephants must first learn the correct sounds to be able to communicate. In these species there are also indications of grammatical rules in communication between conspecifics. The structures and content in the animal kingdom are probably not as complex as in human language, but research is only just beginning and there may still be one or two surprises waiting for us,” OeAW researcher Hoeschele says.