Turbulent space weather disrupts migratory birds

Turbulent space weather disrupts migratory birds

The sun’s activity can change terrestrial magnetic field patterns that migratory birds use to orient themselves. © Artwork by John Megahan, University of Michigan, from Gulson-Castillo et al. in PNAS, October 2023

Not only strong winds but also stormy space weather can cause problems for migratory birds, a study documents: their ability to orientate themselves at night based on their magnetic sense suffers when the Earth's geomagnetic patterns are disrupted by turbulent particle flows from the sun. The data analyzes show that many migratory birds apparently take a break in such conditions.

In autumn they fly south on certain routes and in spring they return purposefully to their traditional breeding areas in the north. As studies have shown, the amazingly precise orientation skills of migratory birds are based, in addition to visual factors, on a sense of the Earth's geomagnetic patterns. They adapt their flight behavior to the learned characteristics of the magnetic field lines on their routes. Especially during their nocturnal flight activity, the birds can use these geomagnetic maps to keep themselves on the optimal course in their heads.

But Earth's magnetic field patterns are known to be not entirely constant: they can change due to large fluctuations in the intensity of the solar wind. It is a stream of charged particles that, in combination with the earth's magnetic field, is noticeable, among other things, in the northern lights. When solar activity increases, this stream of particles can reach high densities and energies and lead to significant distortions in the earth's magnetic field patterns, studies show. There is already evidence that this effect can irritate migratory birds on their long-distance journeys. But the research team led by Eric Gulson-Castillo from the University of Michigan in Ann Arbor has now investigated this connection in more detail for the first time.

Bird migration data linked to geomagnetic information

Their findings are based on long-term data collection on annual bird migration in the United States, whose characteristics are similar to those in other parts of the Earth's Northern Hemisphere. The area examined was a more than 1,600-kilometer stretch of the important migration corridor across the Great Plains - from Texas to North Dakota. Many different species of migratory birds travel there every autumn and spring. Their groups were regularly detected by radar stations along the way. The researchers explain that the data shows the number of birds and the direction of flight. Weather information collected at the same time was also included in the data collection.

The scientists were then able to correlate this information with simultaneous recordings of geomagnetic patterns in the region. The clear disruptions that can be attributed to temporary increases in solar activity became apparent. The researchers then had all the data evaluated by a computer system in order to show the possible effects of the geomagnetic patterns shaped by space weather on bird migration.

How distorted magnetic fields affect

“Our results show that fewer birds migrate under strong geomagnetic disturbances and that migratory birds may have more difficulty navigating at night, especially in cloudy conditions,” concludes Gulson-Castillo. Specifically, the team found a decrease in the number of birds in flight by up to 17 percent in the fall and spring when geomagnetic patterns were disrupted by turbulent space weather.

Apparently some of the feathered long-distance travelers do not want to expose themselves to impairments to their ability to navigate. Observations, especially in autumn, showed that the birds allowed themselves to be driven by the wind more in the event of geomagnetic disturbances than to stay on the optimal course by actively flying against the air current. This was particularly noticeable when the sky was overcast at the same time. The effort required to fly correctly against the wind was then reduced by up to 25 percent, according to the evaluations. This in turn indicates that migratory birds can use a combination of geomagnetic information and visual stimuli in the night sky for their orientation.

The study has now provided further insights into the mysterious navigation abilities of migratory birds, say the scientists: “Our results show how the behavioral decisions of these animals can depend on environmental conditions - including those that we as humans cannot perceive, as in this case of geomagnetic disturbances,” says Eric Gulson-Castillo.

Source: University of Michigan, specialist article: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2306317120

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