It is well-known that birds and other animals depend on the Earth's magnetic field for long-distance navigation during their migration seasons. A recent study reveals that periodic magnetic field disruptions can affect the reliability of biological navigation systems.
Challenge in Nocturnal Bird Migration
Researchers at the University of Michigan tested for the possible connection between geomagnetic disturbances and nocturnal bird migration. They used massive, long-term datasets from the U.S. Doppler weather radar stations and ground-based magnetometers in measuring the intensity of local magnetic fields.
Previous studies about geomagnetic disturbances focused on geographic extent, duration, and the number of species produced. In contrast, the UM team used a 23-year dataset of bird migration across the U.S. Great Plains to provide new insights at population and landscape levels.
Experts used the images gathered at 37 NEXRA radar stations in the central flyway, which spans over 1,000 miles in the U.S. from Texas to North Dakota. The scientists selected this relatively flat region to ensure minimal influences from mountainous topography or oceanic coastlines. The community of nocturnally migrating birds in this area primarily comprises a group of perching birds, shorebirds, and waterfowl.
The team discovered a 9% to 17% reduction in migrating birds during strong geomagnetic disturbances in spring and autumn. Meanwhile, bird species that chose to migrate during such events experience more difficulty navigating, especially under overcast conditions in fall. As a result, these birds may spend less effort navigating in flight and tend to drift with the wind more frequently instead of exerting great efforts to fight crosswinds.
The study showed correlational evidence for previously unknown relationships between geomagnetic disturbances and nocturnal bird migration dynamics. According to study lead author Eric Gulson-Castillo from the UM Department of Ecology and Evolutionary Biology, their research highlights the dependence of animal decisions on environmental conditions, including those that humans cannot perceive. Such behaviors are also found to influence population-level patterns of animal movement.
READ ALSO: Migration Pattern of Birds Are Getting Disrupted By Climate Change on a Continental Scale
Causes of Geomagnetic Disturbances
A geomagnetic disturbance, also known as a geomagnetic storm, refers to a worldwide disturbance of the Earth's magnetic field due to a solar storm. It is a major event in Earth's magnetosphere caused by sudden strong variations in the solar wind's density, speed, and magnetic properties. This period of rapid magnetic field variation can last from hours to days.
Basically, geomagnetic storms have two main causes. Sometimes, the Sun releases a strong surge of solar wind known as coronal mass ejection (CME). This burst of solar wind disturbs the outer portion of the Earth's magnetic field and generates electric current in the near-Earth space environment.
On some occasions, the Sun's magnetic field directly links with that of the Earth. When this direct magnetic connection happens, the charged particles that travel along magnetic field lines can easily enter the magnetosphere, where they generate currents and cause time-dependent variation of the magnetic field.
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