The longer days of spring mean no more commuting in the dark for us. But for millions of migrating birds, nighttime is the only time to travel—they need the dark night sky to navigate thousands of miles home for the summer.
Bird expert Henrik Mouritsen says night-migrating songbirds find their way northward using a combination of enhanced night vision and an internal compass that can sense and create a visual map of the invisible magnetic field surrounding the earth.
"Birds do head-scans in order to sense the earth's magnetic field, so they turn their head sort of from left to right and then from right to left," says Mouritsen, from the University of Oldenburg, in Germany
As he wrote in the journal Proceeding of the National Academy of Sciences, Mouritsen set up cages with Garden Warblers and European Robins—distantly related migrating songbirds. During the day they moved around aimlessly, but at night the birds all behaved in a very distinctive way.
"These birds will sit and fly on the perch, so to say in the direction they wanted to fly outside," he explains.
Working with Duke University neurobiologist Erich Jarvis, Mouritsen compared his birds' brains to Zebra Finches and Canaries, which don't migrate. They discovered that a region, called Cluster-N, at the front of the brain was only active at night.
"This brain area wasn't exclusively used for sensing magnetic fields but instead it's being used to perhaps see at night," says Jarvis.
The researchers believe the birds' ability to sense the Earth's magnetic field and transform it into a navigation tool is dependent of their ability to see at night. "Covering the eyes completely blocked most of the activation in this brain area," he explains.
They think the same part of the brain may also help the birds navigate using the stars.
Jarvis says that although people may have a brain area like this, it's certainly not as developed as in these birds. So don't you be a bird brain and forget your map when you hit the road.
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