새들의 노래에 깃든 여덟가지 기본 가락 [오철우의 과학풍경]

A recent discovery of the xeno-canto.org website has proven to be quite intriguing. This site houses millions of recordings of wildlife sounds worldwide, primarily contributed by amateur nature observers. In addition to the familiar sounds of local birds within apartment complexes, the database contains recordings of 3,160 species of birds across 116,600 sound files.

A recent study published in Science analyzed these bird calls and found that they share common sound motifs. The researchers categorized these basic sounds into eight distinct types: trembling (trill), shrieking, tremolo, whistling, dissonant chords, and multi-toned, disordered sounds. They also discovered that larger birds tend to use simpler, monotonous sounds, while smaller birds with smaller beaks prefer more complex, rapidly changing sounds.

When plotted on a global map, the distribution of bird sounds reveals further interesting patterns. In dense tropical rainforests, where sound dispersal is limited, simpler, monotonous sounds and melodies are more common. In contrast, in open temperate regions where communication over short distances is frequent and competition for mating is intense, more complex sounds with higher information content prevail.

Of course, individual birds do not exclusively use a single sound. The study found that each bird species uses an average of four different sounds, with 65% of the analyzed songs being a combination of multiple sounds. The combination and modification of these basic sounds allow birds to create unique vocalizations for various purposes, such as attracting mates, warding off competitors, and warning of dangers.

However, the specific bird sounds one hears are not solely determined by the bird's condition and environment. Observations from field experiments suggest that bird sounds can also be culturally transmitted and popular within a population. A researcher in Argentina even sought to revive an old bird song that was widely popular in the 1960s but has since been forgotten.

By installing acoustic devices in a park where many young birds gather and playing tapes of the old song, the young birds began to mimic it. The following year, adult birds began to modify the old song in their own unique way. These findings remind us that the once-familiar bird sounds we often take for granted may not be as simple as they seem.

To truly appreciate the natural world, one must first develop a mindful and attentive approach to listening to and observing the sounds around us.