№ 156/2014 from May 08, 2014
Members of the Biocommunication Group at Freie Universität Berlin recently published their findings about nightingale song in two different papers. Just in time for this year’s breeding season, scientists in the group of Silke Kipper, assistant professor of biology, were able to contribute to a better understanding of how songbirds encode messages and how their communication functions. In the study published as "Singing onstage: Female and male common nightingales eavesdrop on song type matching" in Behavioral Ecology and Sociobiology, the scientists analyzed the criteria used by male and female nightingales to choose preferences based on singing duels of males. "The use of network analysis to study complex animal communication systems: A study on nightingale song" was published in the prestigious Proceedings of the Royal Society B and describes a network analysis of the long vocal sequences of nightingales.
In complex and diverse vocal duels, male nightingales frequently do song matching, in which a bird sings a stroph and his opponent responds with the very same one. Considering that every male can sing almost 200 different strophes, the matching is not an accident, but is most likely also aimed at listeners, namely male and female conspecifics. For the study, vocal interactions with frequent song matching were simulated on computers and broadcast to male and female nightingales.
The scientists found that both males and females turned more quickly and more frequently toward the loudspeaker that represented the leader in vocal matching. They interpreted the female's attention as mating interest and that of listening males as response to aggression or dominance behavior. The researchers concluded that when studying the communication of nightingales, observing the listening birds is just as important as those directly interacting.
Male nightingales sing their different strophes – on average about 180 – in different orders, whereby the sequence order is not random. The scientists suspected that information is contained in the order of the strophes, similar to the syntax of human language. They applied a basic network analysis by assigning song types as the nodes or vertices and first-order transitions between song types as edges of the network. This approach – known from studies of complex social structures and logistics systems – enabled a detailed analysis of the vocal networks and, in particular, the so-called nodes or transitions between individual verses.
The calculations showed remarkable differences between the nightingales. For example, it turned out that singing networks are associated with the age of males: older males sing their sequences more orderly. Thus, females can choose a male of a certain age, based on the sequence order of his singing. Furthermore, in vocal duels, the males adjust their strophes or nodes to those of their opponent. This means that they can more easily take over the leadership in a vocal interaction.
Overall the findings make it possible to draw conclusions about the organization of song in the brains, thus providing the behavioral biologists with new starting points for studying the neural foundations of the songbirds' behavior. The researchers at Freie Universität are using both studies as the basis for further experiments.