Migratory songbirds embark on long voyages to return to their mating areas, sometimes spanning continents, and arrive with incredible precision each year.
In order to better understand how birds determine when and where to stop migrating, researchers studied nearly a century’s worth of data and discovered that the Eurasian reed warbler – a songbird that migrates between sub-Saharan Africa and areas throughout Europe each year – uses slight variations 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 lengthy migrations to their mating territories – voyages that occasionally span continents – and arrive with incredible precision each year.
While much research has gone into understanding how these creatures learn and navigate migratory pathways, it has remained a mystery as to how they determine when and when to stop migrating.
Birds are believed to navigate by using cues derived from properties in the Earth’s magnetic field – magnetic declination, inclination, intensity, and overall strength for a given area.
The magnetic field of the Earth, on the other hand, changes somewhat year to year, implying that the magnetic characteristics used to define an individual’s birth and the breeding site will occur in a slightly different area each year.
Despite this, many bird populations are able to return to within a few meters of their natal places each year. Joe Wynn and colleagues analyzed more than 80 years of ringing records for Eurasian reed warblers to see if variations in the Earth’s magnetic field might predict variation in the areas to which birds migrate.
The findings show that while changing their breeding site, birds use magnetic inclination, or the particular dip angle between Earth’s magnetic field and Earth’s surface, like a “stop sign.” Birds learn the inclination angle before leaving these places, which is then employed as a uni-coordinate indication that they’ve arrived when they return, according to the authors.
Although numerous locations on Earth’s surface can have the same inclination, Wynn et al. show that birds solve this by stopping at the first place on their inherited flight itinerary where the correct inclination is encountered.
Source: 10.1126/science.abj4210
Image Credit: Getty
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