Birdsong can make people feel more at ease, yet some calls clearly charm human listeners more than others. A small new study offers clues about the acoustic qualities that may shape those preferences.

Researchers at the University of Tübingen in Germany found that people generally favored softer bird sounds with narrower frequency ranges. More complex vocalizations also received stronger pleasantness ratings, challenging the intuitive idea that simpler, repetitive sounds would be more appealing.

The preference did not appear to depend on participants having extensive knowledge about birds. Dr. Nadine Kalb, the study’s lead author, said the result suggests that enjoyment of birdsong may reflect something more fundamental than recognizing the source.

The study, published September 1 in the journal Frontiers, asked 84 people to listen to recordings from 123 wild bird species. Participants rated how pleasant they found each species’ vocalizations.

The common blackbird, also called the Eurasian blackbird, emerged as the clear favorite. Its rich, mellow and flutelike song earned an average rating of 4.52 out of 5.

Common blackbirds, known scientifically as Turdus merula, are typically seen in gardens, parks and woodlands across Europe. The European goldfinch followed with a score of 4.26, while the European robin received 4.04 and the blue tit earned 3.92.

The barn owl landed at the opposite end of the rankings, receiving an average score of 1.32. Its vocalization is described as an eerie, raspy screech, a sharp contrast with the more melodic calls favored by listeners.

After collecting the ratings, researchers compared them with the acoustic characteristics of each recording. The goal was to connect the biology of bird vocalization with the psychology of human perception and identify features associated with pleasantness.

One of the study’s more surprising results involved complexity. Senior study author Dr. Christoph Randler said the team might have expected simple and repetitive sounds to be easier and therefore more pleasant, but more intricate songs tended to receive better ratings.

Kalb said pleasant birdsong cannot be reduced to one formula or a single acoustic quality. The blackbird, willow warbler and blackcap sound different from one another, yet each received high pleasantness ratings.

Instead, the findings point to combinations involving frequency, amplitude and bandwidth. Different arrangements of those characteristics can produce sounds that listeners consider highly pleasant, according to Kalb.

The research could eventually influence how city planners and park designers approach noisy environments. Rather than concentrating only on reducing unwanted noise, officials might also consider the natural sounds that people hear in parks, urban green spaces and other places used for relaxation.

Randler cautioned that the work remains in its early stages. His team’s previous research found that playing additional birdsong through loudspeakers did not provide greater wellbeing benefits than birdsong occurring naturally.

Dr. Olga Feher, an associate professor of psychology at the University of Warwick in England, was not involved in the research. She said the findings suggest that at least some biological factors contribute to human preferences for birdsong, while personal experience can also shape individual reactions.

Feher studies zebra finches, whose quick, robotic songs are often considered unpleasant, but she enjoys them because of positive associations. She also warned that emphasizing charismatic species with melodious songs could harm conservation efforts involving birds whose vocalizations people find less appealing.

Other research cited by Feher has found possible connections across human and animal sound preferences. A March study reported that humans and other animals tend to share preferences for certain vocal sounds, while a 2020 study found rhythmic patterns shared by human music and birdsong.

Dr. Robert Lachlan, an animal communication researcher and associate professor of psychology at Royal Holloway, University of London, said the study opens a new area of inquiry. However, he said more research is necessary to determine precisely why certain birdsongs appeal to people.

Lachlan questioned whether songs with higher frequencies are always more attractive, observing that blackbirds and nightingales often use relatively low pitched, flutelike notes. He also suggested that biology, familiarity and personal experience probably influence how listeners respond.

The researchers now want to understand why human brains favor particular acoustic combinations and whether those preferences remain consistent across cultures and environments. For now, the findings show that birdsong can attract attention, stir positive feelings and make people more aware of surrounding biodiversity.