It’s well-known that birds and other animals rely on Earth’s magnetic field for long-distance navigation during seasonal migrations.

But how do periodic disruptions of the planet’s magnetic field, caused by solar flares and other energetic outbursts, affect the reliability of those biological navigation systems?

University of Michigan researchers and their colleagues used massive, long-term datasets from networks of U.S. Doppler weather radar stations and ground-based magnetometers—devices that measure the intensity of local magnetic fields—to test for a possible link between geomagnetic disturbances and disruptions to nocturnal bird migration.

They found a 9%-17% reduction in the number of migrating birds, in both spring and fall, during severe space weather events. And the birds that chose to migrate during such events seemed to experience more difficulty navigating, especially under overcast conditions in autumn.

The new findings, published online Oct. 9 in Proceedings of the National Academy of Sciences, provide correlational evidence for previously unknown relationships between nocturnal bird migration dynamics and geomagnetic disturbances, according to the researchers.

“Our findings highlight how animal decisions are dependent on environmental conditions—including those that we as humans cannot perceive, such as geomagnetic disturbances—and that these behaviors influence population-level patterns of animal movement,” said study lead author Eric Gulson-Castillo, a doctoral student in the U-M Department of Ecology and Evolutionary Biology.

Earth’s magnetic field is regularly impacted by solar outbursts that can trigger colorful auroras and that sometimes disrupt satellite communications, human navigation systems and power grids.

But little is known about how those disturbances affect animals that depend on Earth’s magnetic field for migratory orientation and navigation. Previous experimental studies over several decades provide strong evidence that birds, sea turtles and other organisms key into small changes in magnetic inclination, intensity and declination when making orientation decisions and developing navigational maps.

One recent study examined millions of bird banding records and found that geomagnetic disturbances were associated with increased incidence of migratory bird “vagrancy,” that is, birds becoming lost during migration.

But most previous studies were narrowly focused in geographic extent, duration and the number of species examined. The newly published study, in contrast, uses a 23-year dataset of bird migration across the U.S. Great Plains to provide new insights at population and landscape levels.

The researchers used images collected at 37 NEXRAD radar stations in the central flyway of the U.S. Great Plains, a major migratory corridor. The flyway spans more than 1,000 miles in the U.S., from Texas to North Dakota.

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