Turtles Breathe Through Their Butts
Vent Breathing Through Cloacal Bursae
In a previous post I talked about the difference between hibernation and brumation in turtles. Essentially turtles don't sleep all winter, they have punctuated periods of activity. However, turtles do not brumate under water, they usually dig burrows or bury themselves in leaf litter or mud to overwinter. One of the questions I'm asked frequently is, "How do turtles breathe while they are buried?" A similar question was, "How can that turtle breathe while napping under water?" (This was usually aimed at a local terrapin that lived in a tank in the education center). The answers are similar.
Turtles can respire, or breathe, in three main ways:
1. Through their lungs. Turtles are vertebrates and they have lungs, which is their primary means of respiration. This is why sea turtles can drown if they don't come up for air. The crazy thing is, their shell is their rib-cage. Their lungs, guts, organs, legs, everything sit inside their rib cage. Look carefully at the inside of a an empty turtle shell and you can see the fused rib sutures.
The challenge of this type of outer-rib-cage-shell is that unlike you and I, they can't take a deep breath in, expanding their body cavity and lungs, to take a breath like humans do.
I was once asked if a turtle moving its throat was a way of breathing or pumping air into its lungs. You can find LOTS of misinformation about this on the internet. Research has shown that bucal (cheek) pumping and gular (throat) pumping does not correlate to lung inflation (check out this great paper from U Mass Amherst to learn more and see awesome X-rays). Throat movement, in turtles, is more likely associated with smelling or olfaction. Scientists were partly cued into the "smelling" idea because turtles still pump their throats under water, even when they can't take oxygen into their lungs (they plug their throats with their tongue). Throat pumping under water allows for aquatic smells to enter through the nose and mouth even though their throat is closed for diving. This leads to point #2 below.
2. Through their mouths and throats. Stick with me here, and don't get confused. I mentioned earlier that turtles pump their throats and mouths, but it's not pumping air into their lungs. However, some species of aquatic turtles can absorb oxygen through their mouth/throat system. If an aquatic turtle is under water it can move its throat and mouth to take in water to smell and also absorb oxygen across the surfaces inside its mouth/throat complex. The same is true above water. The membranes of the throat and mouth are usually moist, which also allows for oxygen diffusion.
3. Through their butts. Yes, some species of aquatic turtles can breathe through their butts. Now this isn't like the butt-snorkel idea that I wrote about with how mosquito larvae breathe (tubes in their butts held at water level). This much more about oxygen absorption across tissues, and less like breathing through a snorkel or nose. Turtles have what I call the "common poop chute," meaning they poop, pee, mate, and lay eggs through one hole, technically called a cloaca (clo-ay-ka) or vent. In some species of aquatic turtle there are structures called cloacal bursae, which are essentially highly vascularized (filled with blood vessels) tissues which allow oxygen to be absorbed across them. In some species of turtles there are many ridges or folds lining the vents, which also allow for oxygen absorption. How much can a turtle breathe through it's butt? Well, this varies, usually not a lot (>20%). Billy's little turtle in the aquarium isn't going to be OK if you don't let it come up for air, it needs to breathe through its lungs. Of course there are always exceptions, mostly with soft shelled turtles.
The Australian White-throated snapping turtle, also called the "bum-breathing turtle" can get nearly 70% of its oxygen through its cloacal bursae, or butt. Unfortunately this species is critically endangered and may not be around long.
No matter how you shake it, turtles are amazing survivors. Their natural adaptations for respiration are fascinating. If you're leading a lesson or unit on turtles, consider integrating information about turtle respiration. It's easy enough to throw a turtle shell into a trail-pack. You can use it to create a "filler" activity while waiting for groups, or stragglers on a hike, by asking students to compare how they breathe in and out (filling their lungs) to how turtles breathe. It's up to you to add the butt breathing or not, but the kids will LOVE it!