Migratory birds use a magnetic “compass” to know exactly where and when to end their migration, according to a study led by the University of Oxford. Thanks to nearly a century of data with tracked species, the team was able to assess how birds use signals from the Earth’s magnetic field as an indicator of when and where to stop.
It’s not news that migratory birds can travel enormous distances to return to their birthplace or breeding place, but exactly how this happens was a mystery until then.
These birds have biological devices called magnetoreception, which allow them to know which direction to go, where to land to reproduce and nest — and with great precision.
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The new study investigated whether birds also use signals from the magnetic field, such as magnetic tilt — the angle between the Earth’s magnetic field and its surface — or magnetic intensity, the field as a whole.
The researchers used 17,799 records of banded birds from 1940 to 2018 to analyze how the migratory reed warbler (Acrocephalus scirpaceus) used magnetic information for long journeys.
If Earth’s magnetic field varies throughout the year, the researchers said such changes would also be reflected in the gradual transition in the position of areas where birds nest.
Birds “see” Earth’s magnetic field
The results indicated that magnetic tilt is the main information that birds use to return to mating or nesting sites (when building their nests). It is as if specific parameters of inclination signal to the bird the moment to stop.
In addition, the researchers pointed out that the magnetic inclination would be the signal that varies the least, hence the high precision that these species have in finding such places again during migration. So, with their biological mechanisms, these migratory birds are able to use the Earth’s magnetic signals to migrate safely and successfully.
The study was published in the journal science.
