Humans may feel more at ease when they hear birds singing, but some bird sounds sound especially beautiful to the human ear. Scientists are beginning to understand the reasons behind this.
A new, small-scale study reveals that some acoustic characteristics may explain why humans find some birds' songs more beautiful than others. The results, reached by researchers at the University of Tübingen in Germany, showed a tendency among participants to prefer softer, quieter bird sounds with limited bandwidth. At the same time, they considered more complex and diverse sounds more attractive and enjoyable.
The scientists also found that this preference was not related to the extent of the listeners' familiarity with birds or their prior knowledge of them.
“This enjoyment of bird song is related to something more fundamental than simply knowing what type of bird you are listening to,” said Dr. Nadine Kalb, lead author of the study published September 1 in the journal Frontiers.
Kalb is a biologist at the University of Tübingen.
The blackbird topped the list
The research team asked 84 people to listen to recordings of the voices of 123 species of wild birds, and to rate how sweet each bird's voice was.
The blackbird (or Eurasian blackbird) was the star of the survey, receiving an average rating of 4.52 out of 5.
This bird, whose scientific name is Turdus merula, is a common sight in gardens, parks and forests across Europe, with a rich, sweet, flute-like song.
On the other hand, the barn owl came at the other end of the list, as its sounds received an average rating of only 1.32, as the calls of this owl are characterized by their harshness.
So, what makes one bird's voice sound sweet, while another's voice sounds less attractive? This question was at the heart of what the study's lead author and professor of biology at the University of Tübingen, Dr. Christoph Randler, sought to understand.
The researchers wanted to examine the sounds themselves more closely, by combining "the biology of bird sounds with the psychology of human perception," Randler said.
After participants were asked to rate the birds' songs, the researchers compared those ratings to the vocal characteristics of the songs to determine which features made them sound sweeter.
Randler noted that one of the most surprising results was that people tended to prefer more complex bird songs. “Intuitively, we might expect simple, repetitive sounds to be easier to receive and therefore more enjoyable, but the opposite was the case: more complex sounds received higher ratings,” he said.
Paying attention to birds singing
The researchers believe that these findings may help city planners and park designers adopt a different perspective when dealing with noisy places in the future.
Instead of focusing exclusively on reducing noise levels, officials could pay more attention to the nature of the sounds people hear, including natural sounds made by birds.
But Randler stressed that the research is still in its early stages, and simply adding more bird sounds to public spaces may not be the best solution.
Previous research by his team showed that broadcasting more recordings of bird sounds over loudspeakers did not provide welfare benefits beyond those provided by natural bird song.
In this context, Dr. Olga Fehr, associate professor of psychology at the University of Warwick in England, who specializes in studying bird songs, said, “The results indicate that there are biological factors that play a role in bird songs that humans prefer.”
Fehr was not involved in the new study.
Fehr noted that other research suggests that some of our responses to sounds may have deep evolutionary roots: A March study found that humans and other animals often share a preference for certain sounds, while a 2020 study found that human music and bird song share specific rhythmic patterns.
For her part, Kalb stated that the results indicate that there is no single specific formula for the bird’s pleasant sound; “The sounds of blackbirds, willows, and hawksbills are very different from each other, yet they all get very high ratings for being pleasant,” she said.
She added: “Our results do not revolve around one vocal characteristic in isolation, but rather confirm that the combination of frequency, amplitude, and bandwidth are all important factors in determining the palatability of a bird’s voice.”
