Music maintains a characteristic balance between repetition and novelty. In a recent study, scientists reported a similar balance in singing performances of free-living Australian pied butcherbirds.
The finding is published in Royal Society Open Science. Researchers from Hunter College, CUNY, Macquarie University in Australia, Freie Universität in Germany, and New Jersey Institute of Technology conducted the study.
They found that the bird songs included many phrase types. Moreover, the more phrase types in a bird’s repertoire, the more diverse the singing performance could be.
However, without sufficient temporal organization, avian listeners may find diverse singing performances difficult to perceive and memorize.
In the study, researchers tested the correlation between the complexity of song repertoire and the temporal regularity of singing performance in the birds.
The result showed that different phrase types often shared motifs (notes or stereotyped groups of notes). These shared motifs reappeared in strikingly regular temporal intervals across different phrase types, over hundreds of phrases produced without interruption by each bird.
Researchers then developed a statistical estimate to quantify the degree to which phrase transition structure was optimized for maximizing the regularity of shared motifs.
They found that transition probabilities between phrase types tended to maximize regularity in the repetition of shared motifs, but only in birds of high repertoire complexity.
Conversely, in birds of low repertoire complexity, shared motifs were produced with less regularity.
Researchers suggest that the strong correlation between repertoire complexity and motif regularity shows that the butcherbirds possess a mechanism that regulates the temporal placement of shared motifs in a manner that takes repertoire complexity into account.
This is the first study that demonstrates that in one species of songbird that the overall repertoire complexity of the bird is ‘balanced’ by regularity in temporal structure.
Researchers hope that their methods for high-throughput analysis across entire singing performances of wild birds will facilitate studies testing for similar effects in other species.
Citation: Janney E, et al. (2016). Temporal regularity increases with repertoire complexity in the Australian pied butcherbird’s song. Royal Society Open Science, 3: 160357. DOI: 10.1098/rsos.160357.
Figure legend: This Knowridge.com image is credited to Tatiana Gerus.