Weather turns birds into more flexible singers

Sydney, Aug 5 (IANS) Songbirds exposed to fluctuating weather for a long time become more flexible singers, suggests a new study.

Researchers from the Australian National University (ANU) and the National Evolutionary Synthesis Centre analysed song recordings from more than 400 male birds spanning 44 species of North American songbirds - a data set that included orioles, blackbirds, warblers, sparrows, cardinals, finches, chickadees and thrushes.

They used computer software to convert each sound recording - a medley of whistles, warbles, cheeps, chirps, trills and twitters - into a spectrogram, or sound graph, the journal Biology Letter reports.

Like a musical score, the complex pattern of lines and streaks in a spectrogram enable scientists to see and visually analyse each snippet of sound.

For each bird in their data set, they measured song characteristics such as length, highest and lowest notes, number of notes, and the spacing between them, according to an ANU statement.

When they combined this data with temperature and precipitation records and other information such as habitat and latitude, they found a surprising pattern - males that experience more dramatic seasonal swings between wet and dry sing more variable songs.

"They may sing certain notes really low, or really high, or they may adjust the loudness or tempo," said co-author Clinton Francis of the National Evolutionary Synthesis Centre.

The Pyrrhuloxia or desert cardinal from the American southwest and northern Mexico and Lawrence's goldfinch from California are two examples.

Species that experience more extreme differences in precipitation from one location to the next across their range sing more complex tunes. House finches and plumbeous vireos are two examples, Francis said.

"Precipitation is closely related to how densely vegetated the habitat is," said co-author Iliana Medina of Australian National University. Changing vegetation means changing acoustic conditions.