Seven Ways That Terrapins Have Evolved

In my recent post about the terrapin conservation project at The Wetlands Institute, I wrote that terrapins are are the only species of turtle adapted to live in the brackish water of coastal wetlands. This makes them different from sea turtles, freshwater turtles, and tortoises (which live on land).

Evolutionary biologists have calculated, based on differences in their DNA, that terrapins diverged from freshwater turtles around 7 to 11 million years ago. Their nearest relative is a type of freshwater turtle known as a map turtle.

Presented for your enjoyment, seven ways that terrapins have evolved to live in brackish (semi-salty) water:

1. Highly developed lachrymal glands - In humans, these are commonly called tear glands. Human tears are a little salty, but terrapin tears are twice as salty as sea water. This helps flush out excess salt that they have ingested. Sea turtles do the same. People have seen sea turtles "crying" as they lay their eggs on the beach, and assumed it was the pain of childbirth that was causing them to cry. They are just getting rid of their extra salt. Crocodiles have developed a similar mechanism, which is where the term crocodile tears originated.
   
   
2. Specially shaped lower jaw - Terrapins prefer to drink fresh water, since it saves them the trouble of getting rid of the excess salt (and I'm sure it tastes better). When it rains, terrapins will drink from puddles on the ground, collected on leaves, and even collected in the nooks and crannies of their friend's shells. The lower jaw of the terrapin has evolved into a sloping, scoop shape without a "chin". This allows them to drink from puddles as shallow as 1 mm. The box turtle needs a puddle at least 5 mm deep to get a drink.


3. Drinks like a camel - Camels and terrapins have a similar problem - access to fresh drinking water. They have developed a similar adaptation - the ability to quickly drink a large amount of water when it becomes available. A terrapin can drink up to 15% of his body weight in 15 minutes. That would be like me chugging 4 gallons of water! Even better, if the terrapin is attacked by an enemy after a drinking binge, it will regurgitate its water before fleeing. Between the surprise of the barf and the lighter load to carry, this may give the terrapin the edge it needs to escape.


4. Skims the top of the water - When it rains, a layer of fresh rain water collects on the surface of the brackish water. Using a behavioral adaptation, the terrapin will drink from this top layer before it mixes with the rest of the water.


5. Catches falling rain drops - I had a hard time believing this one, but I did read it in more than one reputable source. I think a terrapin would have to be pretty loaded up with salt, and it would have to be raining pretty hard, for this behavior to be worth the effort.


6. Strong jaws - Terrapins can break into some of the tough food found in coastal wetlands, including clams and periwinkle snails (their favorite NJ invasive species).


7. Webbed feet - Midway on the evolutionary scale between the stump-like feet of land tortoises and the flippers of sea turtles, terrapins have webbed feet adapted to their middle-of-the-scale environment.

Chukar Partridge on Mount Haleakala

The chukar partridge is a type of bird known as an "upland ground bird". This means that it prefers the "uplands", away from the water, and prefers being on the ground. Other types of birds perch only briefly, spending much of their time in the air. Some birds love water; swimming, wading and diving. Upland ground birds are happy just walking around.

The chukar in the photo above was giving a new meaning to "upland". I found him almost 2 miles up, on Mount Haleakala in Maui, Hawaii. Like other upland ground birds, chukars are good eatin'. They were introduced into the United States as a game bird from their native Pakistan, where they are the national bird. (Don't laugh - Benjamin Franklin suggested the turkey, another upland ground bird, for the national bird of the United States. At least the birds of the US and Pakistan get along better than the people!)

Being such popular game birds and not very good at flying, chukars are known for their speed in running. Not as fast as that famous upland ground bird the roadrunner (meep-meep), but pretty fast. Since Mount Haleakala is in a national park, maybe this particular chukar was not used to being chased by hunters. He let me walk right up and take his picture. Or maybe he was just trying to obey the posted rules of the park:


According to Pakistani legend, the chukar is deeply in love with the moon, and stares at it longingly. If that is true, my bird picked a good place to live. Mount Haleakala is well known for its clear, dry, still, dark night air. Astronomers from around the country and around the world have set up telescopes here. They have learned what the chukar already knows about the great view of the moon from Haleakala.

Enjoy the sunset below, with the telescopes of "Science City" to the left and a crescent moon just starting to appear to the right. My chukar is sitting somewhere on that hill waiting for his love.

Terrapins vs Toyotas

The Diamondback Terrapin gets its name from the pyramid-shaped bumps on its upper shell, which look like diamonds studding its body. Unfortunately for the terrapin, its shell is not as hard as a diamond.

Terrapins leave their coastal wetlands home for only one reason - to lay their eggs. They slowly scratch their way to higher, drier ground, which can sometimes be far from the water. On their way, they often cross paths with another animal going the other direction, toward the beach for sun and fun.

Luckily for terrapins in New Jersey, they have friends at The Wetlands Institute. Students and volunteers in the institute's programs have constructed fences along coastal roads, to help keep the terrapins off the pavement. When one does get on the road but doesn't make it across, they remove any viable eggs from the body and incubate them for later release. And when terrapins lay their eggs on the institute's property, they cover the nest with a mesh enclosure to keep predators away from the eggs and newly hatched babies.

My son's Boy Scout troop visited The Wetlands Institute on a day when they were removing terrapins from two predator enclosures. The photo below shows an enclosure with its top removed, and a student getting ready to dig out the hatchlings.


And here they are, fresh from their sandy nests. They will spend the rest of the day in their Rubbermaid residence, safe inside the building. They will be released into the bay at night while the hungry seagulls are sleeping.


If you are ever near Stone Harbor, New Jersey, I'm sure you would enjoy a visit to The Wetlands Institute. You can visit their terrapin conservation website here to learn more about these animals. Terrapins are the only species of turtle adapted to live in the brackish water of coastal wetlands, as opposed to sea turtles, freshwater turtles, and tortoises (which live on land). You can even "Adopt-A-Terrapin"!

If you aren't lucky enough to be at The Wetlands Institute when they are rescuing terrapins, you can still have a ball sloshing around in the mud on their nature "trail".


Top photo courtesy of Wikimedia

The Post of the Modern Mariner, or Seagulls Following Boats

And a good south wind sprung up behind;
The Albatross did follow,
And every day, for food or play,
Came to the mariner's hollo!

The Rime of the Ancient Mariner
by Samuel Taylor Coleridge

Like the albatross led the ancient mariner out of Antarctica, the seagull above led us modern mariners across the bitterly cold and windy New York Bay. It was almost too cold to stand on the outside deck, except that the view of the Manhattan skyline, the Statute of Liberty, and the bustling tugs and barges was too captivating.

The huge gusts of wind tossed this poor gull about, but amazingly he was able to steer himself, avoiding crashing into the boat and occasionally even dipping down to snatch up a fish filleted by the boat's propellers. Like the albatross, he seemed to be both playing in the wind and picking up some easy food. He never had to flap his wings, he only used them as rudders to navigate the air currents.

If you look at the photo above, you might feel you were still in the 18th century with Coleridge. I'm sure the boat we were on was not as romantic as Coleridge's tall-masted sailing ship, but it was still pretty nice. You can judge for yourself from the photo below.

And I couldn't resist throwing in a completely unromantic photo, but one that really shows a feeding frenzy of seagulls. The photo below is on the Elizabeth River in Virginia, on a tour of the Norfolk Naval Station. The tour boat, followed by a tug and a container ship, chopped up enough fish to cause a seagull riot.