Habitat and evolution shape the unique sounds of birds

Birds sing, call, and chirp for various reasons – finding mates, fending off predators, or simply enjoying their melodies. But what shapes the diversity of bird sounds remains a fascinating mystery.

Researchers at the University of Wisconsin-Madison set out to unravel this enigma. Their study is shedding light on why birds produce specific sounds and at what frequencies.

The many sounds of birds

Birds produce a wide variety of sounds, each serving distinct purposes in their daily lives. Songs, often complex and melodic, are primarily used by male birds during mating seasons to attract mates or establish territory.

Calls, simpler and shorter than songs, help with everyday communication, like warning of predators or coordinating with flock members. Some species use mimicry, imitating sounds from their environment or other animals to confuse threats or attract mates.

Others, like woodpeckers, create drumming sounds by pecking on surfaces to signal territory. This diversity in sounds reflects birds’ adaptability and creativity in navigating their environments and interactions.

A global first in bird sound research

The study was led by doctoral student H.S. Sathya Chandra Sagar and Professor Zuzana Buřivalová. The team analyzed over 100,000 bird audio recordings from xeno-canto, a global bird-watching repository.

The recordings represented 77% of known bird species, making this research the most comprehensive exploration of bird acoustics to date.

The findings, published in the journal Proceedings of the Royal Society B, revealed key insights into how habitat, geography, body size, and beak shape influence bird sounds.

What shapes bird sounds?

The study highlighted several important patterns:

Habitat influences sound frequency

Birds adapt their calls to ensure they are audible in different environments. For instance, in areas with rushing water, the constant sound creates low-frequency background noise that could drown out their calls.

To overcome this, birds sing at higher frequencies, which stand out against the lower-pitched noise of the water. This adaptation helps them effectively communicate with other birds despite the challenging acoustic environment.

Geography shapes sound similarities

Birds living in similar geographic regions, such as those at the same latitudes, often produce comparable sounds. This pattern indicates that environmental factors specific to these areas – like climate, vegetation, or available food – influence how birds develop and use their calls.

These similarities provide valuable insights into the evolutionary processes that shape bird communication, showing how their sounds adapt to the unique challenges and opportunities of their habitats.

Body size and beak shape

Smaller birds make higher-pitched sounds, while larger birds produce lower ones. Interestingly, small birds can also make a wider range of sounds, using high-pitched calls to communicate and low-pitched ones to confuse predators about their actual size.

For example, canaries and wrens use high-pitched calls for communication, while owls and crows produce low-pitched sounds for territory and long-distance signaling.

Soundscapes and conservation

This research not only improves our understanding of bird communication but also broadens insights into soundscapes – the combination of all sounds in a specific environment, including bird calls, water, and wind.

Soundscapes are valuable tools in conservation because they reflect the health and biodiversity of ecosystems.

“There’s very little that we know about the forces that govern soundscapes,” noted Sagar. By identifying missing low-frequency sounds, researchers could infer human impacts, such as hunting, on larger bird populations.

Future research directions

Sagar plans to build on his research by analyzing 24-hour soundscape recordings to study how birds adapt the timing of their songs in noisy environments. This approach could reveal how birds navigate communication challenges in habitats filled with competing sounds.

Citizen scientists and birdwatchers play a key role by contributing recordings to platforms like xeno-canto, expanding the global data available for analysis.

Sagar also emphasized the connection between bird calls and human impacts. In regions like the tropics, where larger birds are often hunted for meat, the absence of low-frequency calls – typical of larger birds – could indicate increased hunting activity.

This research not only lays the groundwork for future studies but also provides a novel way to monitor ecosystem health through soundscapes.

By understanding the patterns in bird sounds, scientists can gain deeper insights into biodiversity, conservation, and the pressures affecting wildlife. Every recorded bird call brings us closer to uncovering the secrets of the natural world’s complex soundscape.

The study is published in the journal Proceedings of the Royal Society B Biological Sciences.

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