Latest finding - Behavioural Biology
- Twisting tongues: parakeets, like humans, use their tongues when vocalizing
Speech is one of the properties that make humans unique in the animal kingdom. However, it has been proven to be unexpectedly difficult to pinpoint the exact features that make speech special, not least so because of recent discoveries of many parallels between birdsong and human speech. Both are learned behaviors and there is a growing body of evidence that the underlying perceptual mechanisms for birdsong and speech are the same.
However, there are clear differences in vocal production. While humans mainly use their tongue and lips when articulating sounds, songbirds rapidly open and close their beaks and expand the esophagus whereas there is no evidence for tongue movements during birdsong production. Yet, one group of birds might claim the exception that proves the rule. Parrots and parakeets, renowned for their ability to mimic human speech, have prominent, flexible tongues with many muscles that might allow them to use their tongues as vocal articulator when calling. Direct evidence for this hypothesis, however, has been lacking up to now. In a recent study published in The Journal of Experimental Biology researchers from the IBL, in collaboration with the Max-Planck-Institute for Ornithology and Indiana University Bloomington, collected X-ray recordings of calling monk parakeets. Their analysis shows that these birds not only open their beaks, but also move their tongues downward when producing so-called contact and greeting calls. However, when producing chatter sounds, a series of two short alternating notes, the birds move their tongues in a cyclical motion and adjust the relative timing of tongue movements. Furthermore, by placing metal markers on the trachea of some birds, the researchers noticed that the distance between these markers shortened by as much as 44%. This is the first evidence for tracheal shortening during vocal production in parakeets although the effect this has on the sound remains subject to further studies. Nevertheless, one particularly important articulatory movement appears to be missing in the monk parakeets. Unlike humans, these birds do not adjust the back-front position of their tongues much, but mainly change tongue height. However, it is unclear if this observation holds for all of the nine different calls these birds produce or only applies to the subset of three call types that the researchers were able to record. Further research and especially X-ray recordings of speech-imitating parrots will shed more light on the mechanisms of speech production.