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Umwelt -- Loggerhead Turtle




If you stretch a wide ribbon around the middle of the earth, you have found the habitat of the Loggerhead turtle. They swim in the Atlantic, Pacific, and Indian Oceans, staying in the temperate and tropical regions. And they do swim it; females have traveled 8,000 miles to reach their home beaches and lay their eggs. They are reptiles that need to breathe air and lay their eggs on land. But they breathe differently than we do; they can hold their breath for up to seven hours and slow their heartbeat to nine minutes between beats to conserve oxygen. Loggerheads are the second largest sea turtle behind the massive Leatherback. Loggerhead's shell size is about 40", and it weighs an average of 300 pounds. They have evolved a streamlined shell and long front flippers to powerfully pull them through the water, using their smaller back flippers as rudders. They live 70-80 years, and females reach sexual maturity in their thirties. Unlike some other sea turtles, mating time can become violent, with competing males fighting and none-too-gentle mating. Loggerhead shells are small habitats, with up to fifty species living on them. The turtles were named for their large, broad heads, which carry powerful jaws to crunch the hardest shell of their prey.

Their sensory world, their Umwelt, is not overwhelming in the first five senses, but the sixth sense is incredible. Their small eyes do an adequate job for the turtle. Their definition is low, but they can see some of the longer color wavelengths into near ultraviolet. Their ears are behind their eyes and are covered by scales, skin, and fat layers. One would think not much audible sound would make its way through, but low-frequency sound does. From this, the turtle can hear an abundance of communication going on in the ocean, some traveling for thousands of miles. Loggerheads have nerves that run along their backs and can sense changes in water pressure and vibrations, alerting them to possible predators. Divers report the soft parts of Loggerhead's bodies are sensitive to touch (possibly one-handed divers.) Chemoreception is achieved through a combination of smell and taste, coming together as an acute method of locating food and navigation, helping females to find their home beaches and hatchlings find their way to the ocean and the algae mats they will live on.

Their sixth sense is the magnetic sense. Scientists do not fully understand how this sense works in turtles or the many other creatures that have it. Loggerheads can sense the earth's magnetic field and determine their position and directional information. It has been called a GPS, but it seems more reliable than that. The turtles take this information and put a magnetic map in their heads. It seems it is not a generalized map but a precise one with subtle variations in long navigation.

I feel a bit left out in not getting the magnetic sense. I am directionally inept, and this superpower could have saved me from many a problematic and embarrassing situation.


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