Songbirds use build-in GPS to migrate across USA

Posted 7 november 2007

38-year-old researcher Kasper Thorup, University of Copenhagen, has come a step closer to unravelling the secret of how migration birds navigate across large distances. He has followed the birds’ passage across USA from small sports planes. The results are now being published in the scientific journal PNAS.

Every year, millions of songbirds cover thousands of kilometres to spend winter in a mild climate. Biologist Kasper Thorup has participated in a large American research project on how the migratory songbirds find their way across these long distances; in this case from the American East Coast to the northern West Coast in Washington State. It is the first time researchers have followed the birds over such a long distance.

Older birds navigate better

"The project clearly showed that the older songbirds immediately found the right course, whereas the younger birds had more trouble because they ”only” had their natural build-in compass to navigate from. But that wasn’t sensitive enough to find the way home. The young birds did have a sense of the passage, but they couldn’t adjust for the wrong course. Su they probably never reached home. However, the older birds have an almost global navigation system, which makes it possible for them to find their destination and to adjust the course on the way where needed, says Kasper Thorup.

What makes this project stand out is that the birds were equipped with a small transmitter which could be located and followed from small planes. The 30 white-crowned sparrows that were included in the experiment were brought by plane from their migratory passage in Washington State to Princeton University, New Jersey and then set free. The experiment was to see if they could find their way back to their original passage on the West Coast.

It was surprising to see how fast and safely the older birds were able to navigate back towards their winter quarters, just as it was surprising to see how the younger birds were not able to make course-corrections on their way, as they are used to navigate across great distances.

”The experiments show that the older birds’ “GPS” work across very great distances. But the fact that they were removed in a different direction from their passage makes it difficult for them to navigate using the earth’s magnetic field. Therefore it is still a puzzle how exactly their navigation works. Maybe they use the sun, moon and start or maybe they use their sense of smell. So the next step is to test these possibilities”, says Kasper Thorup.