When birds are chirping, humans may feel a little more at ease.. But some bird vocalizations seem to strike a particularly pleasing chord with human ears — and scientists are beginning to understand why. For much of our evolutionary history, the sounds of birds going about their business may have been a reassuring signal that the surrounding environment was free of danger. Now, a small new study has revealed that certain acoustic qualities may help explain why humans find some birdsongs more pleasant than others. People tended to prefer softer bird sounds with a narrower frequency range, while also rating more complex vocalizations as more pleasant, according to researchers at the University of Tübingen in Germany. And the preference didn’t appear to depend on whether listeners knew much about birds, the scientists found. “This suggests that enjoyment of birdsong is connected to something more fundamental than just knowing what you are listening to,” said Dr. Nadine Kalb, lead author of the study published Sept. 1 in the journal Frontiers, in a statement. “Our results show that the combination of various acoustic features is important for how much we like a bird song, and that different combinations of these acoustic characteristics can result in very pleasant sounds,” added Kalb, a biologist at the University of Tübingen, in an email. The researchers said the findings could provide a better understanding of how birds shape our environment — and eventually help inform the design of parks, urban green spaces and other places where people go to unwind. “Perhaps the most important takeaway is that paying attention to birds can change the way we experience the natural world,” senior study author Dr. Christoph Randler said. “Even when we do not understand what a bird is communicating, its song can attract our attention, evoke positive feelings and make us more aware of the biodiversity around us.” Why the common blackbird took top honors The research team asked 84 people to listen to recordings of 123 wild bird species and rate how pleasant they found each bird’s vocalizations. The star of the survey, with an average rating of 4.52 out of 5, was the common blackbird (or the Eurasian blackbird). Typically spotted in gardens, parks and woodlands, Turdus merula is a familiar sight across Europe, with a song that’s rich, mellow and flutelike. At the other end of the spectrum was the barn owl, whose vocalizations received an average rating of 1.32. The barn owl’s call is an eerie, raspy screech. Among other surveyed birds, the European goldfinch received a pleasantness score of 4.26 out of 5, followed by the European robin at 4.04 and the blue tit at 3.92. What makes one bird sound pleasant and another less so? That question was at the heart of what Kalb and Randler, a professor of biology at the University of Tübingen, wanted to understand. “Our interest developed from a broader question: why do some encounters with birds feel particularly positive to people? In our previous research, we had already found that birds and birdwatching can contribute to psychological restoration and well-being,” Randler said in an email. This time, the researchers wanted to look more closely at the sounds themselves — bringing together “the biology of the bird’s vocalization and the psychology of human perception,” Randler said. After asking people to rate the birdsongs, the researchers then cross-referenced the ratings with the songs’ acoustic characteristics to determine which features made them sound more melodic. One of the most surprising findings, Randler said, was that people tended to prefer more intricate birdsongs. “We might intuitively expect simple, repetitive sounds to be easier and therefore more pleasant, but the opposite pattern emerged: more complex sounds tended to receive higher pleasantness ratings,” he noted. Paying attention to birdsong The findings could eventually help city planners and park designers think differently about noisy places, according to the researchers. Instead of focusing only on reducing noise, officials could also pay more attention to the kinds of sounds people hear, including natural ones such as birdsong. But Randler stressed that the research is still in early days — simply adding more birdsong to spaces may not be the answer. Playing extra birdsong through loudspeakers did not provide greater well-being benefits than naturally occurring birdsong, his team found in previous research. “It reminds us that bird vocalizations have an important dimension beyond communication between birds: they also form a major part of the soundscape experienced by humans,” Randler said. Dr. Olga Feher, an associate professor of psychology at the University of Warwick in England who studies birdsong, said, “The findings suggest that there are at least some biological factors in human birdsong preference.” Feher was not involved with the new study. Feher pointed to other research that suggests some of our responses to sound may have deep evolutionary roots. A March study found that humans and other animals tend to share preferences for certain vocal sounds, while a 2020 study uncovered that human music and birdsong share certain rhythmic patterns. But personal experience can also shape those preferences, Feher said. She studies zebra finches, whose fast, robotic songs are often considered unpleasant, “but I really like them myself, no doubt due to the pleasant associations,” she said in an email. She added that while the new paper suggests we can use the information to improve the design of acoustic environments for humans, a focus on charismatic species with melodious songs can have a harmful effect on conservation efforts for those with less pleasant songs. “To me, the most interesting thing about this research is that it tells us something about the evolution of our perception of beauty, and that this is something we share with certain songbirds who sing to entertain and impress their conspecifics,” Feher said, referring to members of the same species. Dr. Robert Lachlan, an animal communication researcher and associate professor of psychology at Royal Holloway, University of London, said the study opens the door to a new area of research, but more work is needed to understand exactly what makes some birdsongs appealing to humans. He questioned whether higher-frequency songs are necessarily more attractive, noting that birds known for beautiful songs, such as blackbirds and nightingales, often use relatively low-pitched, flutelike notes. “I’d not be surprised if there are regions of the frequency scale, for example, that we tend to find more attractive,” Lachlan said. This preference might not have been detected by looking only at the highest and lowest frequencies in the songs, he added. He noted that biology and personal experience are also likely to shape how people perceive birdsong. “I think that it was interesting that birding experience had no effect on which songs were found to be attractive in this study,” Lachlan said in an email. “I think there are other dimensions here — I know I feel differently when returning home from traveling and hear familiar birds in my neighbourhood.” Kalb, lead study author, said the findings suggest there is no single formula for a pleasant bird sound. “The blackbird, willow warbler and blackcap sound quite different from one another, yet all received very high pleasantness ratings,” she said. “Our findings are not about one acoustic feature in isolation, but rather that the combination of frequency, amplitude and bandwidth is important for how pleasant a bird sound is perceived.” Randler agrees that there is more work to be done. “The study establishes which acoustic characteristics are associated with pleasantness; it does not yet tell us exactly why our brains prefer those characteristics,” Randler said, adding that the next step is to understand why people prefer certain birdsongs and whether those preferences hold across different cultures and environments.
