Researchers undertook a comprehensive global study examining what influences bird sounds, analyzing more than 100,000 audio recordings sourced from across the globe.
Birds produce sounds to communicate with each other, whether it’s to attract mates, deter threats, or simply for enjoyment.
However, the factors that lead to the wide variety of sounds birds produce are not entirely clear. At the University of Wisconsin-Madison, a team led by researchers has executed the first global investigation into this issue, utilizing over 100,000 bird sound recordings from around the world. This new research, published in the journal Proceedings of the Royal Society B, uncovered valuable insights regarding why birds emit specific sounds and the frequency at which they do so.
While previously tested theories concerning the effects of habitat, location, body size, and beak shape on bird vocalizations were limited in scale, H.S. Sathya Chandra Sagar—a doctoral candidate at UW-Madison—sought to evaluate these ideas on a global platform, collaborating with Professor Zuzana Buřivalová from the Department of Forest and Wildlife Ecology and the Nelson Institute for Environmental Studies.
Sagar meticulously examined recordings of bird sounds contributed by enthusiasts worldwide, which were collected in a bird-watching database called xeno-canto. The analyzed sounds represented 77% of all recognized bird species.
Key findings from the study included:
- The habitat of bird species affects the frequency of their sounds in unforeseen ways. For instance, within environments characterized by significant rushing water, there exists a consistent background noise at lower frequencies, prompting birds to produce higher frequency sounds to avoid being overshadowed by the noise of the water.
- Bird species located at the same latitudes produce similar sounds. This pattern observed globally adds a crucial component to the evolutionary narrative surrounding bird sounds, potentially opening avenues for more research into geographic features shaping vocalizations.
- The shape of a bird’s beak and its body mass play vital roles. Typically, smaller birds tend to create higher frequency sounds, while those that are larger produce lower frequency sounds. This global analysis not only confirmed this theory but also offered new insights into how beak shape, body size, and sound are interconnected.
- Smaller bird species generally possess a broader range of frequencies in their calls, serving as a protective strategy. These smaller, more exposed birds can leverage this diversity in sound; higher frequencies help them collaborate with other individuals of their species, while lower frequencies can camouflage them, misdirecting predators into thinking they are bigger and less at risk.
This study also enhanced the overall understanding of soundscapes—the collective sounds found in specific environments. While soundscapes are commonly analyzed in conservation studies, Sagar noted that “very little is understood regarding the factors influencing soundscapes.”
He hopes that this foundational research will lay the groundwork for future investigations aimed at improving conservation techniques by analyzing the health of ecosystems through soundscapes.
“In tropical regions and worldwide, larger birds are often targeted for their meat,” he exemplifies. “These larger birds typically call at lower frequencies, so if we observe a lack of sound in that range, we might deduce that hunting pressure is higher in that area.”
Looking ahead, Sagar plans to utilize continuous 24-hour recording of soundscapes to determine whether certain bird species adjust the timing of their calls—not just the frequencies—to better communicate in noisy environments. He emphasizes the significant contribution of birdwatchers and citizen scientists in uncovering new insights about the natural world.
