Variations in the Earth’s magnetic inclination are “stop signs” for migratory songbirds

Information on how birds know when and where to stop migration, researchers using nearly centuries-old data, report that the Eurasian warbler, a songbird that migrates each year between sub-Saharan Africa and parts of Europe, uses small changes in the Earth’s magnetic field as a kind of “stop sign” that signals when it has arrived at its destination.

Migratory songbirds embark on long journeys to return to breeding grounds – journeys that can sometimes span continents – and arrive each year with astonishing accuracy. However, while much research has focused on understanding how these creatures assimilate migratory routes and navigate them, it remains a mystery how they know where and when to stop migrating.

Birds are believed to use signals derived from the Earth’s magnetic field parameters – magnetic declination, tilt, intensity and total strength for a specific area – to control their arrival. However, the Earth’s magnetic field shifts slightly from year to year, suggesting that the magnetic parameters used to determine a person’s place of birth and place of reproduction will occur in a slightly different place each year. Despite this, bird populations can still return each year within meters of their birthplaces.

During their migration, reed warblers use magnetic information as a “stop sign” – with a magnetic tilt, in particular, informs the birds that they have arrived at their destination. Author: Thomas Miller

To investigate whether fluctuations in the Earth’s magnetic field could predict changes in bird migration locations, Joe Winn and his colleagues evaluated more than 80 years of ringing records of Eurasian reed reeds. The results show that birds rely on a magnetic inclination or a certain angle of incidence between the Earth’s magnetic field and the Earth’s surface as a “stop sign” when transferring a breeding site.

According to the authors, the birds study the angle of inclination before departure from these places, which is then used as a single-coordinate signal that they arrived after returning. Although several places on the Earth’s surface may have the same slope, Wynn et al. show how birds solve this by stopping in the first place where on their hereditary flight trajectory the correct inclination occurs.

Read more about this discovery Magnetic navigation: a stop sign for songbirds during migration.

Help: “Magnetic stop signs signal the arrival of European songbirds at the breeding site after migration” Joe Win, Oliver Paget, Henrik Muritsen, Joe Morford, Paris Jaggers and Tim Guilford, January 27, 2022, Science.
DOI: 10.1126 / science.abj4210