According to current research, severe space weather events are associated with a 9-17% decrease in the number of migrating birds in both spring and autumn (fall). Solar flares and other explosive outbursts in space produce periodic disruptions to the Earth’s magnetic field, which migratory birds rely on for long-distance navigation. The remaining birds that chose to migrate during such events appeared to have more difficulty navigating, particularly in overcast conditions in autumn, according to researchers from the University of Michigan (U-M) study, which used a 23-year dataset of bird migration across the Great Plains, a major migratory corridor, for analysis.
The radar images or scans detect groups of hundreds to thousands of migratory birds, allowing the researchers to assess migration intensity
“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 behaviours influence population-level patterns of animal movement,” said Eric Gulson-Castillo, lead author of the study published in the journal Proceedings of the National Academy of Sciences.
The researchers examined photos collected at 37 radar stations along the Great Plains’ major flyway, which stretches more than 1,600 kilometers from Texas to North Dakota in the United States. The flat location was chosen for the study to reduce the influence of hilly topography or coastal coastlines. The radar images or scans detect groups of hundreds to thousands of migratory birds, allowing the researchers to assess migration intensity and determine flight direction, according to their study. This region’s nocturnally migrating bird community is mostly made up of perching birds like thrushes and warblers, shorebirds like sandpipers and plovers, and waterfowl like ducks, geese, and swans.
“Effort flying” against the wind was reduced by 25 percent under cloudy skies during strong solar storms in the fall
In total, the datasets for the study contained 1.7 million fall radar scans and 1.4 million spring radar scans. The radar data was then compared to a geomagnetic disturbance index, which measured the maximum hourly change from background magnetic circumstances. The index was created using data from a global network of geomagnetic ground stations. The researchers then used statistical models to assess the effects of magnetic disruptions on bird migration. Along with fewer birds, the researchers discovered that during geomagnetic disturbances in the fall, migratory birds appeared to drift with the wind more frequently, rather than exerting significant effort to combat crosswinds.
That is, “effort flying” against the wind was reduced by 25 percent under cloudy skies during strong solar storms in the fall, suggesting that a combination of obscured celestial cues and magnetic disruption may hinder navigation, they said. “Our results suggest that fewer birds migrate during strong geomagnetic disturbances and that migrating birds may experience more difficulty navigating, especially under overcast conditions in autumn,” said Gulson-Castillo, also a doctoral student in the U-M Department of Ecology and Evolutionary Biology. “As a result, they may spend less effort actively navigating in flight and consequently fly in greater alignment with the wind,” said Gulson-Castillo.
