THE white-tipped plantcutter is a reddish small bird that emits a distinct hoarse groaning sound. It is not a vocal learner, meaning it has little motor control over the sounds it makes. Instead, the bird relies mostly on biomechanics to sing its rasp. Now, researchers studying the biomechanics of the white-tipped plantcutter’s rasp have determined how to gauge the bird’s size through its vocalisations. An Argentinian and German team of scientists, led by Gonzalo Uribarri of the Institute of Physics of Buenos Aires at the University of Buenos Aires analysed recorded birdsongs and employed computational models to assess song segments. They found a relationship between the frequency of resonating sounds from birds’ oro-esophageal cavities and birds’ sizes. The scientists also checked the correlation between song and size by testing museum specimens. The results suggest that the biomechanics of bird sounds could potentially be used to predict bird size. The work was recently published in the journal “Physical Review Letters”.