Language is one of the defining characteristics of human beings: It enables us to generate unlimited meanings from a finite number of phonetic elements. Using syntactic rules, humans are able to combine words to form phrases and sentences, and thus ascribe meaning to various things and activities. Research on communication systems suggests that non-human primates and birds, too, have evolved the ability to assign meaning to arbitrary vocal elements. But until now, the evolution of syntax has been considered unique to human language.
Warning signal plus mating call means “flock together”
Evolutionary biologists at The Graduate University for Advanced Studies in Japan, the Uppsala University in Sweden and the University of Zurich are now challenging this view. For the first time, these researchers have demonstrated that Japanese great tits (Parus minor) have developed syntactic rules. These small birds are known for their large vocal repertoire, and the team discovered that they use a variety of calls and combinations of calls to interact with one another in specific situations. The combination of sounds such as the “ABC calls”, for instance, means “watch out!”. The great tits use them when a sparrowhawk or another predator is nearby – a potentially dangerous situation. By contrast, “D calls” mean “come over here,” a call the birds use after discovering a new source of food or when wanting their partner to come to the nest.
Tits frequently combine these two calls into ABC-D calls when, for instance, the birds encounter predators and join forces to deter them. When hearing a recording of these calls played in the natural order of ABC-D, the birds are alarmed and flock together. When, however, the call ordering is artificially reversed to D-ABC, the birds do not respond.
Generating meaning by combining limited vocabulary
The researchers have therefore drawn the conclusion that syntax is not unique to human language: It has also evolved independently in birds. “The results lead to a better understanding of the underlying factors in the evolution of syntax. Because the tits combine different calls, they are able to create new meaning with their limited vocabulary. That allows them to trigger different behavioral reactions and coordinate complex social interactions,” says Dr. Michael Griesser, at the Institute of Anthropology at the University of Zurich. He believes these factors may well have contributed to the development of language in humans.
Toshitaka N. Suzuki, David Wheatcroft, Michael Griesser. Experimental evidence for compositional syntax in bird calls. Nature Communications. March 8, 2016. doi: 10.1038/ncomms10986