Oxygen Out the Cloaca

Three-toed Box Turtle -  Mark Bower

If you ever wonder how blog topics come up, this is a very good (or bad) example.  A friend in Arkansas who has recently become excited about bird photography sent me the picture below of dabbling ducks on a lake.  For reasons I will leave to your imagination, it elicited a response from Larry Wegmann, asking if I knew that turtle's respiration includes their cloaca.



I thought of this again when I was in the field yesterday fighting weeds around seedling trees.  I stepped on something round in the thick grass.  Pushing back the growth I found a box turtle virtually buried with only the top of its shell showing.  I cleared some dirt around it long enough to see it move some and then left it alone.  How could it breathe with its head buried?

Turtles face several unique challenges in breathing.  Their ribs are fixed to their shell and can't expand to breathe like birds or mammals.  They also lack the absorbent skin of amphibians.  They can't take a big breath like we can as explained at Eoearth.org:

"Turtles cannot expand their chest to breathe because of their rigid bony shells. They inhale by contracting their limb flank muscles to make the body cavity larger and exhale by drawing the shoulder girdle back into the shell, forcing air out of the lungs. " 

When active they need to be able to breathe air through their mouths.  When inactive they tend to spend the winter buried, frequently in a wet environment.  Many turtles spend long periods of time underwater.  During that time they depend on anaerobic metabolism as explained at Discovery.com.  In these cases they can obtain oxygen through tissues in their mouth and cloaca whose lining can function as gills.

"Compare this to the relatively cheap butt breathing. Sacs next to the cloaca, called bursa, easily expand. The walls of these sacs are lined with blood vessels. Oxygen diffuses through the blood vessels, and the sacs are squeezed out. The entire procedure uses little energy for a turtle that doesn't have a lot to spare. Dignity has to play second-fiddle to survival sometimes."

The cloaca is a single opening for intestinal, urinary and reproductive functions found in all amphibians, birds, and reptiles.  It is a handy single orifice which can deliver urine, stool or in females can deliver eggs.  And apparently it can deliver oxygen!

Turtles therefore can survive in airless environments and are apparently not bothered by "bad breath."