Birds may sound different depending, but scientists have now found that many of their songs are built from the same basic set of sound patterns. A new global study has identified eight recurring motifs that appear in the songs of thousands of bird species. It also explains why birds living in forests sing differently from those in open landscapes.According to the research, a birdsong is shaped by both evolution and the environment. A bird inherits many features of its song from its ancestors and the place where it lives also plays an important role. Dense forests, humidity and long communication distances can affect how sound travels, leading birds to use songs that are easier to hear.
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The findings, published in the journal Science, reported Science X, are based on one of the largest studies of birdsong ever carried out. Researchers analysed more than 116,000 song recordings from 3,160 species of passerine birds collected from around the world through citizen science projects.
A global framework for birdsong
Birdsong is more than pleasant background sound. Birds use songs to attract mates, defend their territory and communicate with rivals or neighbours. For these messages to be useful, the sounds must carry information and also travel well through the environment until they reach another bird.Scientists have studied birdsong for many years, but most earlier research focused on simple measurements such as pitch or frequency. According to the researchers, that approach missed many important details that make each song meaningful.In this study birdsongs were treated as information and not just sound. Apart from looking at the pitch, scientists also analysed how both frequency and timing change throughout each song. This allowed them to compare songs from thousands of species using the same method.
Why Passerine birds were chosen
The researchers studied passerines, also known as perching birds or songbirds. Passerines include more than 6,000 species and accounts for over 60% of all bird species on Earth.Also, they are found in almost every land habitat, from tropical rainforests to open grasslands and mountains. Because they live in such different environments, they helped understand how habitats influence birdsong on a global scale.The recordings used in the research came from open-source citizen science databases, allowing researchers to study bird communication across continents.
The study focused on passerines, also known as perching birds or songbirds.
Eight building blocks of birdsong
To compare songs, the scientists used an automated sound analysis method. They examined each recording using modulation power spectrum, which is a techinique to measure how sound changes over time and across different frequencies.According to the analysis, most bird songs are made from combinations of just eight recurring sound motifs. These motifs are building blocks that birds combine in different ways, much like musicians arrange notes into different melodies.The eight motifs include three types of trills played at different speeds, three kinds of whistles with different pitch changes and two more complex sounds described as atonal chaotic notes and harmonic stacks.Most species used more than one motif in their songs. In fact, researchers found that individual songs usually contained between two and eight motifs.However, one motif often dominated. The researchers found that 65.3% of species used their main motif in more than 80% of their songs. The remaining 34.7% of species used a wider mix of motifs, resulting in greater variation in their songs.
Location influences singing
After identifying the eight motifs, the researchers looked at where different song patterns were most common. They found that birds communicating over long distances usually relied on simpler sounds. This included flat whistles and slow trills which travel farther without losing clarity.Birds communicating over shorter distances, on the other hand, often produced faster and more complicated songs. These include ultrafast trills and harmonic stacks, which carry more information. These, however, become distorted more easily as they travel.The researchers say this shows there is a trade-off. Birds can either produce highly detailed songs that carry more information or simpler songs that travel better across long distances.
Birds living in temperate regions used faster and more complex whistles and trills.
Challenges of rainforests and open landscapes
The study also found differences between tropical and temperate regions. Birds living in tropical rainforests generally used simpler songs. Thick vegetation and humid air make it harder for complex sounds to travel without becoming distorted. As a result, birds in these habitats chose sounds that remain clear even after passing through dense forests.In contrast, birds living in temperate regions used faster and more complex whistles and trills. Scientists say that these sounds break down more easily over distance, but the birds use these as they may not need to communicate across such long distances.The researchers believe this difference may also be linked to stronger competition for mates in temperate regions.
Role of evolution
Although habitat affected birdsong, the researchers found that evolution remained the strongest influence. By comparing bird songs with family relationships between species, body characteristics and mating systems, the team found that phylogeny, or evolutionary history, explained 82% of the variation in song motifs.The study also found smaller but consistent differences linked to mating systems. Species in which one male mates with multiple females were more likely to use certain fast-changing whistles and other complex song patterns.This suggests that birdsong develops through a combination of inherited traits, environmental conditions and behaviour.
