As any experienced birdwatcher will tell you, songbirds have distinguishing chirps and tweets that vary from species to species. Some birds have significant neural control over the sounds they produce, and they learn their songs by mimicking older members of their species. However, a group of birds known as tracheophones, which includes the variable antshrike pictured here, will develop adult song even when raised in isolation. Each tracheophone species has a distinctive structure to its tracheal membrane; there are differences not only in its size but also in its collagen–elastin composition, and those differences produce vocalizations at varying frequencies. Until recently, biologists believed the tracheal membranes were largely responsible for the sounds that tracheophones produce.
A new study, however, shows that the tracheal membrane is only one of three sound sources that tracheophones use to produce their songs. Biologists Sarah Garcia and Franz Goller at the University of Utah led...
