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

Bird watchers get very excited when a ‘rare’ migratory bird lands after being blown off course and flying out of its normal range. But these are rare for a reason; most birds that have made the journey before can correct large movements and find their final destination.

Now, new research by an international team shows for the first time how birds moved in this way can navigate back to their migratory route and gives us insight into how they accomplish this feat.

Register in Current BiologyThe team from the universities of Bangor and Keele describes how reed warblers can navigate from a ‘magnetic position’ beyond what they experienced in their normal migration route, back to that correct route.

Different parts of the Earth have a distinct ‘geomagnetic signature’ based on their location. This is a combination of the strength of the Earth’s magnetic field, the magnetic inclination or angle of inclination between 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 common magnetic signatures were kept in captivity for a short period before being released back into the wild, and exposed to a simulation of the Earth’s magnetic signature at a location thousands of miles away. the birds. ‘natural draft.

Despite staying physically in their capture location and experiencing all other sensory clues about their location, including starlight and the sights, smells and sounds of their actual location, the birds still showed the urge to embark on their journey as if they were in the suggested location by the magnetic signal they experienced.

They orientated themselves to fly in a direction that would lead them “back” to their towing path from the location suggested to them by the magnetic signals they experienced.

This shows that the Earth’s magnetic field is the key factor in guiding reed warblers when blown off course.

“The predominant impulse was to respond to the magnetic information they received,” explains Richard Holland of Bangor University’s School of Natural Sciences.

What our current work shows is that birds can sense that they are outside the bounds of the magnetic fields they know from their year-round movements, and that they can extrapolate their position sufficiently from the signals. This fascinating ability allows birds to navigate their normal migration route. “

Dr. Dmitry Kishkinev from Keele University’s School of Life Sciences explained:

What these birds accomplish is “true navigation.” In other words, they are able to return to a known target after moving to a completely unknown location without relying on a familiar environment, signals coming from the destination, or information collected during the outward journey. “

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

But the question remains whether the birds have an accurate ‘map’ or are just using a ‘rule of thumb’ measurement to judge the general direction of travel needed to get back on course.

The Sedge Warbler was selected for the study, but the findings could likely be applied to other migrating songbirds.