title: Vocal tract articulation in zebra finches.
abstract: BACKGROUND
  Birdsong and human vocal communication are both complex behaviours which show striking similarities mainly thought to be present in the area of development and learning. Recent studies, however, suggest that there are also parallels in vocal production mechanisms. While it has been long thought that vocal tract filtering, as it occurs in human speech, only plays a minor role in birdsong there is an increasing number of studies indicating the presence of sound filtering mechanisms in bird vocalizations as well.
  
  
  RESULTS
  Correlating high-speed X-ray cinematographic imaging of singing zebra finches (Taeniopygia guttata) to song structures we identified beak gape and the expansion of the oropharyngeal-esophageal cavity (OEC) as potential articulators. We subsequently manipulated both structures in an experiment in which we played sound through the vocal tract of dead birds. Comparing acoustic input with acoustic output showed that OEC expansion causes an energy shift towards lower frequencies and an amplitude increase whereas a wide beak gape emphasizes frequencies around 5 kilohertz and above.
  
  
  CONCLUSIONS
  These findings confirm that birds can modulate their song by using vocal tract filtering and demonstrate how OEC and beak gape contribute to this modulation.
authors.affiliation: Behavioural Biology, Institute of Biology Leiden, Leiden University, Leiden, The Netherlands. v.r.ohms@biology.leidenuniv.nl
authors.forename: Verena R
authors.initials: VR
authors.lastname: Ohms
authors.forename: Peter Ch
authors.initials: PCh
authors.lastname: Snelderwaard
authors.forename: Carel
authors.initials: C
authors.lastname: Ten Cate
authors.forename: Gabriël J L
authors.initials: GJ
authors.lastname: Beckers
mesh_terms: D000818:Animals; D002933:Cineradiography; D005260:Female; D008297:Male; D020308:Songbirds / Q000502:physiology*; D014828:Vocalization, Animal / Q000502:physiology*