Coiled trachea

["Norton, Patrick" <Patrick.Norton@state.me.us>]

Last summer in the osteology hall of the Smithsonian I observed a   
skeleton of a small crane (recent) with a tracheal tube which descended   
from the mouth to the sternum, formed a complete loop at the top of the   
sternum, then headed for the lungs. My estimate is that the loop made the   
trachea 30-50% longer than it would have been if it were a straight tube.   


My understanding is that the additional length of the trachea is not a   
repiratory impediment for birds due to the nature of avian ventilation   
systems. And I have since been told that the lenghtening of the trachea   
in birds relates to vocalization and can be seen in songbirds as well as   
long-necked birds such as cranes.

It struck me recently that another animal group that had (perhaps) the   
functional equivilent of tracheal loops were the crested, although their   
loops were piled on top of their heads rather than contained within the   
chest. Although many folks have suggested that hadrosaurs used their   
crests in vocalization, I haven't heard any discussion of those   
structures as possibly homologous to the internal tracheal loops of   
birds.

Any thoughts on this?