Early Egyptians took advantage of messenger pigeons' homing abilities, yet the feat of the flying postmen remains a bit of a mystery.
How do birds released in one country find their way home in another, thousands of miles away? In part, they depend on a clock and a compass and they follow their nose. But the whole story is a lot more complicated.
In recognizable territory close to home, pigeons rely on familiar natural and manmade landmarks.
Researchers in Britain have shown that the birds will follow roads and highways, turn at cross streets, and go around roundabouts, even if it means adding miles to their trip. A recent study suggests that pigeons take more efficient paths when flying in pairs, suggesting they're smart enough to take a shorter route if a companion will suggest a good one.
On long-distance voyages, pigeons calculate the direction they need to fly by comparing the position of the sun with their internal clock. By keeping birds under artificial lights, scientists have manipulated the birds' sense of time and tricked them into flying in the wrong direction.
To determine what else steered pigeons toward home, researchers conducted countless experiments, including snipping nerves in the nose. Once the nerves were severed, pigeons could not find their way home, leading scientists to assume the birds literally follow their nose.
However, it's still unclear whether pigeons are always sniffing a course through the sky. They also have two internal magnetic "compasses," thought to be located near the nose and in the eyes, which may help them calculate the Earth's magnetic fields.
Similar compasses, made of iron, have been found in the snouts of rainbow trout.
Animals use all sorts of tools to orient themselves or to map out their migration routes. Chickens have a magnetic compass. Songbirds rely on light from the sun, the stars, and the angle of sunlight, known as polarized light. On their annual fall trip to Mexico, monarch butterflies also use polarized light patterns.
Marine animals often use topographic features and other visual cues on the ocean floor to find their way. Whales pick out these geographic cues with sonar. Research has shown that sharks and sea turtles use electric fields to navigate. Meanwhile, the shallow swim of a shark tracked across the Indian Ocean suggests it might have been watching the night skies for direction.
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