Roaming bird’s secret is its animal magnetism, says scientists

The mystery of the reed warbler’s amazing feat of navigation as it journeys from Europe to Africa has been partially solved by scientists.

It’s believed the reed warbler is genetically hardwired to set out in a certain direction.

Every year, the reed warbler makes an epic journey across two continents.

The voyage from northern Europe to sub-Saharan Africa is a feat of navigation and scientists appear to have unravelled one of the songbird’s tricks: it uses the Earth’s magnetic field as a kind of stop sign to tell it where to land.

It has long been thought that birds make use of the field, generated by the churn of liquid iron far below our feet. Exactly how has remained unclear.

There are three aspects of the field that might help. Its intensity differs from place to place, which might guide a bird capable of sensing it. The angle between magnetic and true north, known as magnetic declination, could also act as a navigational aid.

Finally, there is magnetic inclination, the angle between the magnetic field and the ground. The field is perpendicular to the surface of the Earth at the magnetic poles, and runs parallel to the surface at the equator. If you know the magnetic inclination, you can tell how far north you are.

There is a problem, though, in relying on the field for navigation: it does not stay still. The magnetic north pole wanders the Earth. At present it is drifting eastwards towards Siberia by about 50km a year and the intensity of the field, magnetic declination and magnetic inclination all shift over time.

The Oxford University study drew on about 80 years of data, including information on nearly 18,000 warblers that had been tracked after being ringed. The idea was to see if their migratory routes had altered in a way that gave away what, if any, aspects of the field they rely on. There was one positive result: changes in magnetic inclination matched changes in the birds’ paths.

“Put really simply, they are following inclination around – so when it moves north, they move north; when it moves south, they move south,” said Joe Wynn, the lead author of the study, which was published in Nature.

He believes the birds are genetically hardwired to set out in a certain direction. “We know that is inherited,” he said. “If you take birds that travel in different directions and breed them together, the offspring go in a compromise direction down the middle.”

For the winter, they leave Europe towards Africa. Magnetic inclination, it seems, tells them when they have travelled far enough south. “If you’ve already got this direction of travel, then you only need one more cue,” Dr Wynn said. “You need a sign to tell you where to stop.”

The Times