Disturbances to Earth’s magnetic field can lead birds astray — a phenomenon scientists call ‘vagrancy’ — even in perfect weather, and especially during fall migration. While other factors such as weather likely play bigger roles in causing vagrancy, researchers found a strong correlation between birds that were captured far outside of their expected range and the geomagnetic disturbances that occurred during both fall and spring migrations.Disturbances to Earth’s magnetic field can lead birds astray — a phenomenon scientists call ‘vagrancy’ — even in perfect weather, and especially during fall migration. While other factors such as weather likely play bigger roles in causing vagrancy, researchers found a strong correlation between birds that were captured far outside of their expected range and the geomagnetic disturbances that occurred during both fall and spring migrations.