By Pamela Holz
It stated with a simple question about turtles. While they hibernate in the mud at the bottom of ponds, they still need to breathe, right? So how can they, when they are technically under water for months?
The answer, not so simple, is a combination of the nature of hibernation and turtles? unique adaptations.
First, levels of hibernation can vary. Bear, for example, are light hibernators. They wake up periodically over the winter to take care of basic needs, give birth, etc. Unfortunately for bear researchers, this may also mean they wake up quickly if disturbed.
Other animals enter a deep sleep state. Their metabolism, heart rate, breathing all slow significantly. The shadow-fearing groundhog exemplifies this. Their heartbeat slows to about 4 beats per minute and body temperature drops to around 38 degrees. Thus, the needs of hibernating animals are much less than when active. Turtles need only one-tenth of their active energy to survive over winter. Many cold-blooded animals, such as reptiles and amphibians, need to be deep hibernators. Their cold-blooded, or exothermic, nature simply means they cannot maintain their own body temperature. As a result, they are unable to be active or function at freezing temperatures.
Many of these animals must hibernate in locations that will ? hopefully ? remain above freezing in order to prevent tissue damage and loss. Because of a quirk of water, the temperature at the bottom of the winter pond is 39 degrees. That?s enough above freezing to keep those creepy-crawlies alive.
Some frogs, however, have back-up plans. A few have a type of antifreeze in their blood to prevent such damage. Another one alters its circulation to allow its limbs to freeze without consequence. I can?t help but think those first hops after spring thaw must be rather stiff and awkward.
Turtles also need some unique ways to assist with their hibernation. While their shell might keep them all nice and safe, it simultaneously limits them.
The bottom piece, the plastron, is formed by a fused and fixed rib cage. That means there is much less space for other tasks. Such as breathing.
If you look down and take a deep breath, you will quickly realize the problem. While our chests expand as we inhale necessary oxygen, turtles cannot do the same. Hibernation aside, they already face breathing issues. That may also explain their slow speed of life; they can?t get enough breath to move faster.
One method turtles use to combat their limited ability to breathe and being underwater is to simply stop breathing.
Ok, that?s not so simple as they still need to have some bodily functions remain active to keep them alive. This can actually be done without oxygen, but a side effect is a build-up of dangerous acids.Fortunately their shell is comprised of elements that buffer these acids. In addition, the animal stores the excess acids where it does no harm.
Some turtles have another plan as well. Some of them use the same method frogs do, by breathing through their skin.
A special design of the skin on their throat allows them to absorb oxygen from the water into their bloodstream.
If that?s not enough, a few have what scientists call cloaca respiration.
With the exception of most mammals, all animals with a backbone have a cloaca. This is an all-purpose opening at the hind end.
It handles both forms of waste removal as well as reproduction. And in certain turtles, it helps them breathe.Yes, you read it right. They breathe through their butt.
Special air sacs enable them to ?inhale? water and gain oxygen. This also offsets the limiting lung capacity as well as allows them to breathe underwater. Win-win, right?
So, aren?t you glad you?re not a turtle?
Pamela Holz is the Washington County Conservation Board naturalist.