Internal Compass

Human sailors had a longitude problem. English sailors frequently enough shipwrecked on the coast of England because they did not know where they were east-west wise. The pocket-watch was a huge innovation to improve navigation. GPS even more so improved sailing. (Though I recently watched a GPS put our position on the ocean when we clearly were a quarter mile up a river.)

Birds and reptiles have an internal compass. Move an alligator without putting magnets near her head will just result in her walking and swimming home. This story about loggerhead turtles using magnetic maps is interesting.

To see whether the turtles somehow use magnetic information to decipher east-west direction, researchers recreated ocean-like conditions. They placed hatchlings inside a circular, water filled arena. The space was surrounded by coils to generate a magnetic field. The turtles were tethered to a tracking device that monitored their swimming direction.

When the turtles were exposed to a field like that which exists on the southwest side of the Atlantic, near Puerto Rico, the animals swam northeast, which would take them back toward North America and their normal migration route.

When they were exposed to fields as exist on the northeast side of the Atlantic, near the Cape Verde Islands, they swam southwest. This would again take them to the North American coast.

Since the hatchlings had never been in the ocean, the ability to recognize east-west direction seems to be inherent. “Turtles exploit at least two different geomagnetic features that vary in different directions across the Atlantic,” states the report.

That animals know and understand the differences of the magnetic fields to know where they are located while we do not is so fascinating.

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