Amazingly tuned: Male nightingales cleverly adapt the sound of their performances to the pitches of competing singers, a study shows. Being able to take over confidently seems to go down well with the Vogel ladies or to impress rivals. It's an interesting system of biological intelligence, the scientists say. Because the ability to reflect is probably based on a special circuit in the brain of the virtuoso songbirds.
Instead of colorful feathers, the nightingales enchant us with their acoustic brilliance: the melodic combinations of "flute tones" and rolling clicks stir up emotions in many people. The romantic singing even inspired musical compositions and brought the inconspicuous little birds appearances in world literature. But of course they don't actually sing to please us. Male nightingales use the singing spectacle to attract potential mates and defend their territories against rivals.
The sonorous concept is also interesting from a scientific point of view, because it shows parallels to our communication systems. Therefore, researchers want to know more precisely how the complex sounds of the nightingales are structured, which messages are conveyed and what happens on a neurological level. In the current study, the team led by senior author Daniela Vallentin from the Max Planck Institute for Biological Intelligence in Seewiesen has now dealt with the interactive aspect of nightingale song. It is well known that male nightingales react intensely to rivals - during the mating season, neighbors engage in veritable song duels and seem to be inspired by their respective opponents.
On the trail of vocal contagion
An interesting parallel emerges, say the scientists: "It's very similar to people, who also adapt many characteristics of their voice, such as volume or pitch, to the person they are talking to in the course of a conversation. This behavior helps us have meaningful conversations,” says Vallentin. "We therefore wanted to find out whether nightingales are capable of something similar, i.e. whether they can flexibly adapt their singing behavior to the songs of their competitors," says the researcher. The team recorded the song duels of nightingales during the mating season in their breeding areas in Germany. They then subjected the sound sequences from whistles of different pitches to an acoustic analysis in order to uncover special features.
As they report, they have now been able to document more precisely how the male nightingales sing their song verses in response to the singing of rival neighbors. Accordingly, they imitate the pitch of the opponent over a wide frequency spectrum. The reflecting singing behavior became particularly clear through manipulated models: The singers even tried to adapt to melodies played over loudspeakers with artificially generated singing elements that lay outside the normal spectrum of the nightingales.
Neuronal singing secrets in sight
The nightingales most closely imitated the song frequency of their competitors when they responded directly to their songs. If the answer came with a little delay, they were less precise, the scientists found. "This indicates that the frequency adjustment is carried out using a special neural circuit. There is probably a direct connection between the sensory brain area, in which the heard song is processed, and the motor area, which is responsible for song production," says lead author Giacomo Costalunga.
In addition to their investigations in the breeding grounds of nightingales in Germany, the researchers then also carried out experiments in the wintering quarters of migratory birds in West Africa. It turned out that although the birds there usually hardly ever sing, they surprisingly also reacted to played sounds with a response that was tuned to the pitch. This could indicate that the ability to flexibly adjust song is not only useful during courtship. The scientists say that it may play an important role throughout the year, for example in defending a territory.
As the researchers explain, this result also provides clues to the neural basis of the system: "The neural circuitry that underlies this ability does not appear to be affected by seasonal changes in the same way as the circuitry that controls other aspects of song says Costalunga. The researchers now want to devote more time to the neural background: They plan to uncover more precisely what goes on in the heads of the top stars of the world of songbirds during their performances.
Presentation video for the study with sound samples. © Costalunga et al. Current Biology, doi: 1016/j.cub.2023.06.044
Source: Max Planck Institute for Biological Intelligence, specialist article: Current Biology, doi: 1016/j.cub.2023.06.044