Fiddler crabs take carefully calibrated steps to find their way home, according to a new study in Current Biology [subscription required]. Scientists testing the tiny crustaceans’ homing skills found that both the length and number of their strides were guided by some sort of internal mileage counter. This allows them to plot a direct path back to their sandy burrows even if the burrows are out of sight. “We were able to measure every step by every leg of every animal in this experiment, and since these are eight-legged animals, that’s a lot,” [Scientific American] says co-author John E. Layne.
Many animals appear to have built-in GPS systems, although exactly how they function is not well-understood. Birds and sea turtles may use the position of the stars and the earth’s magnetic field to navigate. The honeybee has been shown to use the flow of the passing landscape across its field of vision. Some other animals may be able to gauge linear acceleration and use that to determine distance [The New York Times]. The way animals keep track of their movements and the distance they’ve traveled is known as path integration.

The secret to a dolphin’s speed is sheer strength, according to a new study that used high-tech measurements to finally put a 70-year-old conundrum to rest. In 1936, British zoologist James Gray incredulously observed dolphins swimming at speeds of over 20 mph. He estimated that the dolphins should only be able to produce a tenth of the necessary force and imagined that something about the dolphins’ skin allowed them to overcome the force of drag in the water and reach high speeds. “For the first time, I think we can safely say the puzzle is solved,” said [researcher] Tim Wei…”The short answer is that dolphins are simply much stronger than Gray or many other people ever imagined.” [
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An
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