Birds can ‘read’ Earth’s magnetic signature well enough to get back on track

Bird watchers are very excited when a “ rare ” migratory bird touches land after being deviated from its path and flown beyond its normal range. But these are rare for a reason; most birds that have made the trip are able to correct large movements and find their final destination.

Now, new research from an international team is showing for the first time how birds displaced in this way are able to return to their migratory route and giving us insight into how they accomplish this feat.

Write in Current biology, the Bangor and Keele University team describes how reed warblers can navigate from a “magnetic position” beyond what they experienced on their normal migration route, back to that correct route .

Different parts of the Earth have a distinct “geomagnetic signature” depending on their location. It is a combination of the strength of the geomagnetic field, the magnetic tilt, or the tilt angle between the magnetic field lines and the horizon, and the magnetic declination, or the angle between directions to the geographic and magnetic north poles.

Adult birds already familiar with their migration route and general magnetic signatures were held in captivity for a short time before being released back into the wild and exposed to a simulation of the Earth’s magnetic signature thousands of miles away. – beyond birds. “Natural migratory corridor.

Although they remain physically located at their capture site and know all other sensory cues about their location, including starlight and the sights, smells and sounds of their actual location, birds have always had the need. to begin their journey as if they were at the suggested location. by the magnetic signal they were subjected to.

They oriented themselves to fly in a direction that would bring them back to their migratory path from the place suggested to them by the magnetic signals they felt.

This shows that the Earth’s magnetic field is the key factor in guiding reed warblers when they get out of their way.

“The primary impulse was to respond to the magnetic information they received,” explained Richard Holland of the School of Natural Sciences at Bangor University.

What our current work shows is that birds are able to sense that they are beyond the limits of familiar magnetic fields through their movements throughout the year, and are able to sufficiently extrapolate their position from the signals. This fascinating ability allows birds to navigate their normal migration route. “

Dr Dmitry Kishkinev, from the School of Life Sciences at Keele University, explained:

“What these birds achieve is ‘real navigation.’ In other words, they are able to return to a known goal after being moved to a totally unfamiliar location without relying on their familiar surroundings, on signals. that emanate from the destination or to information collected during the outward journey. “

Florian Packmor from Bangor University added: “We have already shown that reed warblers use the same magnetic signals that are experienced in their natural range, but this study shows that they can extrapolate what they understand to the way the magnetic field varies in space far beyond any previous experience they’ve had. “

But questions remain as to whether the birds have an accurate “map” or simply use a “rule of thumb” to judge the general direction of travel needed to get back on course.

The Eurasian Reed Warbler was selected for research, but the results could likely be applied to other migratory songbirds.