Herons don’t just lie, they cheat (or at least their tracheas do)

This beautiful image is bird 52659 from Florida Museum, a green heron Butorides virescens, CT scanned and published on Twitter.

(The scan is apparently from MorphoSource, but I can’t find it there.)

There is lots to love here: for example, you can see that the long bones of the arm are pneumatic, because the margins of the bones show up more strongly than the cores. But you won’t be surprised that I am interested mostly in the neck.

As you can see, while the vertebrae of the neck are pulled back into a strong curve, the trachea doesn’t bother, and just sort of hangs there from the base of the head to the top of the lungs, cheerfully crossing over (i.e. passing to the side of) the vertebral sequence. So the trachea here is not much more than half the length of the vertebral sequence.

Now this is the opposite of what we see in some birds. Here, for example, is a trumpet manucode Phonygammus keraudrenii (a bird-of-paradise) as illustrated in Katrina van Grouw’s book The Unfeathered Bird:

Yes, all those coils visible in the torso are the trachea, which is many times longer than it needs to be to connect the head to the lungs. Birds-of-paradise do this sort of thing a lot (Clench 1978).

And they are not alone: cranes and others also have elongated and contorted tracheal trajectories. So it’s odd that herons seem to do the opposite.

But the heron is even odder than that. As we have noted before, herons can stretch their necks out to the point where you would scarcely believe the unstretched and stretched animals are the same thing. But they are:

The CT-scanned heron at the top of this post is in a pose intermediate between the two shown here. But since it can adopt the long-necked pose on the right, it’s apparent that the trachea can become long enough to connect the head and lungs in that pose. Which means it must be able to stretch to nearly twice the length we see in the CT scan.

Don’t try this at home, kids!

References

• Clench, Mary H. 1978. Tracheal elongation in birds-of-paradise. The Condor 80(4):423–430. doi:10.2307/1367193