Migratory birds who rely on Earth’s magnetic field to navigate become lost during space weather events such as solar flares, a new study reveals.
Nocturnally migratory birds – such as geese and swans, sandpipers and thrushes – use Earth’s magnetic field as a natural sat nav to guide them during their long seasonal migrations.
But when space weather disrupts the magnetic field, fewer birds choose to fly, the findings show. Those that do often end up disorientated or lost due to the disruptions to their navigation.
The new findings were based on large, long-term datasets that demonstrate for the first time the previously unknown relationship between nocturnal bird migration and geomagnetic disturbances.
Our planet’s magnetic field is regularly impacted by solar outbursts which can trigger colourful auroras and sometimes disrupt satellite communications, human navigational systems and power grids.
However, little is still known about how these disturbances affect animals which depend on Earth’s magnetic field for migratory navigation and orientation.
Previous studies have shown strong evidence that some birds and sea turtles tune into small changes in magnetic inclination, intensity and declination when orientating themselves and developing navigational maps.
One recent study even found geomagnetic disturbances to be associated with increased migratory bird ‘vagrancy’ – birds becoming lost during migration.
But most previous studies were narrowly focused in geographic extent, duration and the number of species examined.
This most recent study, however, used a 23-year dataset of bird migration across the United States’ Great Plains – a huge plateau running the length of the country east of the Rocky Mountains – to provide fresh insights.
The researchers, from the University of Michigan used images collected at 37 radar stations in the central flyway of the US Great Plains, a major migratory corridor.
The Plains extend over more than a thousand miles down the centre of the country, stretching from Texas in the south to North Dakota near the Canadian border.
The final datasets for the study, published in the journal Proceedings of the National Academy of Sciences, included 1.7 million radar scans from the autumn and 1.4 million from the spring.
Communities of nocturnally migrating birds in this region primarily consist of a diverse set comprised of 73% perching birds such as thrushes and warblers, 12% shorebirds including sandpipers and plovers and 9% waterfowl such as ducks, geese and swans.
The researchers matched data from each radar station with a customised index of geomagnetic disturbance representing the maximum hourly change from background magnetic conditions.
The team’s data trove was fed into two complementary statistical models to measure the effects of magnetic disturbances on bird migration. The models controlled for the known effects of weather, temporal variables such as time of night and geographic variables such as longitude and latitude.
The findings revealed that fewer birds migrate during space weather disturbances.
They also found that those that do still migrate drift with the wind more frequently during geomagnetic disturbances in the autumn, instead of expending great effort to battle crosswinds.
‘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 lead author Eric Gulson-Castillo, a doctoral student in the 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.’
The results showed that ‘effort flying’ against the wind was reduced by a quarter under cloudy skies during strong solar storms during the autumn, suggesting a combination of obscured celestial cues and magnetic disruption may hinder the navigation of the birds.
‘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 Mr Gulson-Castillo.
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