Every year, thousands of bird species migrate from Africa to Europe, covering thousands of kilometers. Upon their return, they manage to locate their breeding grounds with remarkable accuracy, often within a few meters. Scientists have now discovered how they achieve this feat. Ornithologists from the UK and Germany have investigated the cause of this remarkable sense of orientation in migratory birds. They report in the journal Science that the inclination, or the angle between the magnetic field line and the Earth’s surface, likely plays a crucial role in their orientation.
The researchers used data from nearly 18,000 ringed reed warblers collected between 1940 and 2018 to study the birds’ orientation. They also analyzed the locally acting geomagnetic field for different areas in large parts of Europe. The scientists considered not only the magnetic intensity but also the inclination and declination, which is the angle between a horizontal component of the magnetic field lines and the geographic north. After analyzing various factors, they concluded that the inclination, coupled with the general south-north orientation of the flight path, provides the birds with the best orientation. The inclination of the locally prevailing magnetic field, which the birds learn from birth, acts like a stop sign or a guide. The inclination orientation resulted in a deviation from the breeding ground of only 1.2 kilometers in statistical analyses. The variations with other parameters of the magnetic field, such as declination and intensity, resulted in significantly larger deviations between 20 and 235 kilometers.
This study provides good evidence that the reed warbler finds its breeding ground through the detected inclination of the Earth’s magnetic field. Further analyses of other migratory bird species could now follow to confirm or reject the inclination thesis.
