Window on Nature
By Lowell & Kaye Christie, F47246
Hennrietta was a houseguest in our motorhome many years ago. We found her “” at least we thought it was a her “” in the middle of the road next to a backcountry campground, and no matter how many times we moved her, she insisted that the road was her personal highway. Whether it was for her safety or to satisfy our own curiosity, she spent the next few days of her life in a large terrarium we kept in our coach.
It didn’t take us long to discover that Hennrietta was sharp-eyed and a quick learner. She could tell the difference between the three other occupants of the motorhome. She stuck her head out when Kaye approached, anticipating a treat, such as a soft berry or a slug (her favorite). She disappeared inside her shell when our curious dog wandered near the terrarium. And she totally ignored the guy with the beard, Lowell. He seldom offered any food.
Hennrietta was a tortoise, and since we were in the Southeast at the time, she was probably a gopher tortoise (Gopherus polyphemus). There are only three species of tortoises in the United States, and the other two, the desert tortoise and the Texas tortoise, live in the West. But how did we know she wasn’t a turtle?
Well, in much of the world, Hennrietta would have been a turtle. It’s only in North America that a distinction is made between “turtles” that live entirely on land (tortoises) and those that spend their lives in and around water (turtles or terrapins).
Because they walk on land, tortoises have strong, thick legs to maneuver over the ground and to support their heavy shell. The desert tortoise that we know from the West has stumpy hind legs and feet that remind us of an elephant.
Turtles, on the other hand, have legs and feet adapted to a watery world. Along with lighter shells “” because they have to swim “” many have long, webbed toes that they spread to press against muddy pond bottoms or to help them move through the water. And sea turtles, the most specialized of the family, have front legs and feet that resemble flippers. The fastest of these “slow” turtles can use their flippers to cruise the oceans at speeds of up to 19 miles per hour. Hennrietta definitely was a tortoise.
We released Hennrietta a few days later, well away from the road, but our fascination with these interesting creatures has remained. Although many turtle species are endangered today, their history extends back more than 200 million years. When the dinosaurs died out, the turtles just kept on living.
Turtles and tortoises are reptiles, and like other reptiles they are cold-blooded, air-breathing creatures. Being cold-blooded, or ectothermic, means their temperature is controlled by their environment. They don’t regulate their body heat by metabolizing food, but rather by moving to a warmer or cooler place. The tortoise will dig a burrow to escape extreme cold or heat. At a top speed of around 0.3 miles per hour, they aren’t likely to migrate very far, considering that their home range spans approximately three-quarters of a mile.
Pond turtles burrow into the mud to escape the cold or climb on a log or rock to catch a bit of sun. And both turtles and tortoises may estivate or hibernate during extreme weather, either hot or cold. Although pond turtles, like the others, need air to survive, during their dormant periods some can absorb enough oxygen from the water to remain submerged in the mud for the entire winter. Oceangoing sea turtles simply swim farther south.
The turtle tribe is a study in contrasts. The desert tortoise lives in areas where water is sometimes just a memory. It survives dry times by storing extra water in its bladder. When the rains finally come, it drinks to slake its thirst and to refill its bladder.
Sea turtles live in water, salty as it may be. But they have developed special glands near their eyes that excrete the salt from the liquid they drink. These saline tears are not noticeable while they are in the water, but when they come ashore, the turtles appear to be crying.
The contrasts are even greater in their home territories. Instead of the three-quarter-mile worldview of the tortoise, the seagoing loggerhead turtle has a migration route around the Atlantic Ocean that stretches 8,000 miles. Hatching as two-inch youngsters on the eastern coast of Florida, they immediately head to water and into the Gulf Stream, which takes them north around the Sargasso Sea.
The loggerhead turtle’s methods of navigation were a mystery for years, but researchers at the University of North Carolina conducted a study that may partially answer the question. Seventy-nine baby loggerheads were placed in a circular tank shortly after hatching. Around the outside of the tank was an electric coil that could generate various patterns of magnetic fields. The scientists found that the direction the young turtles would swim could be controlled by simulating the magnetic pattern from three locations along their migration route. The turtles evidently had inherited a mental magnetic map.
When we imagine a turtle, the first thought is usually of the shell, or carapace. This textured, patterned surface is composed of keratin, similar to the protein that makes up human hair and nails. But even shells among the turtle family are varied. The hawksbill turtle is endangered because of its extremely attractive carapace, which often is used for tortoiseshell jewelry. The leatherback turtle doesn’t really have a hard “shell,” but instead sports a leathery skin covering the bony plates that make up its back.
Even with all this variety, turtles and tortoises have much in common. They all live fairly long lives; one tortoise in captivity survived for more than 180 years. Even some of the moderate-sized turtles can live for more than 50 years. And all turtles and tortoises lay eggs on the ground. This means that even female sea turtles, not designed for locomotion on the land, must find a suitable spot to come ashore where they can bury their eggs in the sand.
Turtles face all kinds of trouble in their quest for survival. One of the most serious is getting caught in fishing nets. If they are stuck below the water’s surface too long, they will drown. And last year, Hurricane Katrina struck during Florida’s sea turtle hatching season.
A lack of appropriate nesting areas is also a concern. The location must be remote, so the eggs will be undisturbed for two to three months before they hatch (some tortoises take much longer than that). The absence of the bright lights that often accompany coastal development is also a requirement. Young sea turtles instinctively head toward the brightest light after they hatch. In a natural environment, that will be toward the water. But if there is artificial illumination in the opposite direction, the baby turtles will take off that way and are unlikely to survive.
If Hennrietta was a gopher tortoise, her lifespan “” as long as she learned to stay out of the road “” could be up to 60 years. She probably still lives within a short distance from where we found her. Gopher tortoises, like many other members of the turtle family, are declining throughout their area and now are listed as threatened or endangered in parts of their range. No longer is it possible to “study” them as we did so many years ago. But if you happen to come across a Hennrietta in your travels, be sure to at least say “Hello.”