Here’s What Scientists Just Discovered
By University of Wisconsin-Madison
Birds produce sounds to communicate—for attracting mates,
deterring predators, or simply singing for enjoyment. However, the factors
driving the vast diversity of these sounds remain poorly understood.
Photo by Will Collette
Researchers at the University of Wisconsin–Madison have
conducted the first global study examining what influences bird vocalizations.
By analyzing over 100,000 audio recordings from around the world, their study,
recently published in the Proceedings of the Royal Society B, uncovers key
patterns explaining why birds make certain sounds and how frequently they do
so.
While previous studies have explored how habitat, geography,
body size, and beak shape affect bird sounds, these investigations were limited
to smaller regions. 
Photo by Will Collette
H.S. Sathya Chandra Sagar, a UW–Madison doctoral student
working with Professor Zuzana Buřivalová in the Department of Forest and
Wildlife Ecology and the Nelson Institute for Environmental Studies, aimed to
test these hypotheses on a global scale.
Sagar analyzed audio recordings of bird sounds taken by
people around the world and submitted to a bird-watching repository called xeno-canto.
The analyzed recordings represented 77% of known bird species.
Key Findings from the Study
The study’s major takeaways included:
- Bird
species’ habitat influences the frequency of the sound they may make, in
unexpected ways. For example, in ecosystems with a lot of rushing
water there is a constant level of white noise occurring at a lower
frequency. In such cases, researchers found that birds tend to make sounds
of higher frequency, likely so they wouldn’t be drowned out by the water.
- Bird
species living at the same latitudes make similar sounds. Observing
this pattern at a global scale is an important piece of the puzzle in the
evolutionary story of bird sounds. It could inspire further research into
the aspects of geographic location that influence bird sounds.
- A
bird’s beak shape and body mass are important. Generally, smaller
birds create higher frequency sounds while larger birds create lower
frequency sounds. The global analysis not only proved this hypothesis
correct, but it also added new information about the nature of the
relationship between beak shape, body mass, and sound.
- Smaller
bird species tend to have a wider range of frequencies at which they can
make sound as a protection mechanism. Smaller, more vulnerable
birds can benefit from being able to make a range of sounds. Higher
frequencies can help them communicate with fellow birds of the same
species, while lower frequencies can serve as a camouflage, tricking
potential threats into thinking they are larger and less vulnerable than
they actually are.
The research also contributed to the broader understanding
of soundscapes — all of the sounds heard in any particular landscape.
Soundscapes are often used as part of conservation studies, but Sagar realized
“there’s very little that we know about the forces that govern soundscapes.”
He hopes this foundational work will provide a platform for
future studies to improve conservation efforts by developing ways to monitor
the health of an ecosystem through soundscapes.
“In the tropics and all over the world, larger birds tend to
be hunted for meat,” he says as an example. “Larger birds [tend] to call at a
low frequency, and if we don’t find any sound in the lower frequency, we could
[conclude] there may be more hunting in this landscape.”
Next, Sagar hopes to use 24-hour soundscape recordings to
understand if some birds modify the timing of their song in addition to their
frequencies to communicate with their peers in a landscape crowded with noise.
And he notes the important role that birdwatchers and citizen scientists play
in discovering new insights about our natural world.
Reference: “Global analysis of acoustic frequency
characteristics in birds” by H. S. Sathya Chandra Sagar, Akash Anand, Maia E.
Persche, Anna M. Pidgeon, Benjamin Zuckerberg, Çağan H. Şekercioğlu and Zuzana
Buřivalová, 31 October 2024, Proceedings B.
DOI:
10.1098/rspb.2024.1908
