Just as the human pattern of speech is dependent on geographic location, birds' songs evolve depending on the island they colonize.
"The Progressive Loss of Syntactical Structure in Bird Song along an Island Colonization Chain"—a study led by postdoctoral associate Robert Lachlan—analyzed the loss of syntax amongst colonizing chaffinches as they moved further away from their island of origin. The findings were published in the journal of Current Biology yesterday.
Each time chaffinches colonized a new island, they lost some of their distinctive syntactical structure, Lachlan found.
"In mainland Europe, chaffinch songs are very distinctive because of the order of their syllables—certain types of syllables, for example, only occur at the end of the song," Lachlan wrote in an email Oct. 3. "By Gran Canaria, however, any syllable could occur anywhere within the song."
Although the researchers do not have one clear favored explanation for this pattern, the results show that song is not evolving in a random pattern in these populations, Lachlan noted.
The research was motivated by an interest in the evolution of cultural behavior like bird song, he added.
"We still do not have a complete idea of how culture and genes interact in evolution, and, in my opinion bird song provides a great model system for rectifying this," Lachlan said. "There are thousands of species of birds that learn their songs and we have growing evidence from a range of sources that, underlying this learning, many genes are involved too."
The discovery is significant because it broadens the field’s understanding of the evolution of animal “language,” said Steve Nowicki, dean and vice provost of undergraduate education and professor of biology. The findings, however, can also be related to man’s cultural evolution.
“[Our] own language also is subject to cultural evolution of course and this work may also eventually provide insight into how human speech dialects change over time,” Nowicki wrote in an email Oct. 2.
Lachlan noted that syntactical structure in bird song could have a genetic basis, and the observations he made could have been the result of “evolution in genetic predispositions underlying learning.” He added that more evidence would be needed to support this theory though.
“We are still [hoping] to prove conclusively that syntax in chaffinch songs has a genetic basis," he said. "We hope that future work will examine this more directly.”Lachlan developed a computer software that enabled him to analyze bird song from 12 populations that he and his colleagues had collected—beginning in 1998 on a number of islands, some of which were very remote.
Carel ten Cate, a co-author of the study, said that Lachlan collected the data a few years ago but needed to develop an entirely new method to analyze the categories of which the songs are constructed and the way the different elements are used to compose song.
Nowicki noted the completeness of Lachlan’s analysis and the surprising conclusion.
“[This] work represents the most detailed analysis of the cultural evolution of an animal signal done to date," he said. "The work reveals a pattern of loss that runs contrary to what one might expect from a functional point of view. Instead of finding increasing complexity with an increased number of species, which is predicted if recognizing the correct species is a driver, Lachlan found that with each subsequent colonization event, complexity was lost,” Nowicki wrote.
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