Mixing it up helps birds ensure that their songs are heard no matter what the habitat, say researchers at Australian National University and the National Evolutionary Synthesis Center.

To test the idea, the researchers analyzed 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. Like a musical score, the complex pattern of lines and streaks in a spectrogram enable scientists to see and visually analyze 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.