Bad weather can sometimes cause birds to become disoriented during their annual fall migrations — causing them to wind up in territory they’re unaccustomed to. But why, even when weather is not a major factor, do birds travel far away from their usual routes?
A new paper by UCLA ecologists explores one reason: disturbances to Earth’s magnetic field can lead birds astray — a phenomenon scientists call “vagrancy” — even in perfect weather, and especially during fall migration. The research is published in Scientific Reports (https://www.nature.com/articles/s41598-022-26586-0)
With North America’s bird populations steadily declining, assessing the causes of vagrancy could help scientists better understand the threats birds face and the ways they adapt to those threats. For example, birds that wind up in unfamiliar territory are likely to face challenges finding food and habitats that suit them, and may die as a result. But it also could be beneficial for birds whose traditional homes are becoming uninhabitable due to climate change, by “accidentally” introducing the animals into geographic regions that are now better suited for them.
Earth’s magnetic field, which runs between the North and South Poles, is generated by several factors, both above and below the planet’s surface. Decades’ worth of lab research suggests that birds can sense magnetic fields using magnetoreceptors in their eyes. The new UCLA study lends support to those findings from an ecological perspective.
“There’s increasing evidence that birds can actually see geomagnetic fields,” said Morgan Tingley, the paper’s corresponding author and a UCLA associate professor of ecology and evolutionary biology. “In familiar areas, birds may navigate by geography, but in some situations it’s easier to use geomagnetism.”
But birds’ ability to navigate using geomagnetic fields can be impaired when those magnetic fields are disturbed. Such disturbances can come from the sun’s magnetic field, for example, particularly during periods of heightened solar activity, such as sunspots and solar flares, but also from other sources.
“If the geomagnetic field experiences disturbance, it’s like using a distorted map that sends the birds off course,” Tingley said.
Lead researcher Benjamin Tonelli, a UCLA doctoral student, worked with Tingley and postdoctoral researcher Casey Youngflesh to compare data from 2.2 million birds, representing 152 species, that had been captured and released between 1960 and 2019 — part of a United States Geological Survey tracking program — against historic records of geomagnetic disturbances and solar activity.
While other factors such as weather likely play bigger roles in causing vagrancy, the 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. But the relationship was particularly pronounced during the fall migration, the authors noted.
Pictures and captions:
https://www.nature.com/articles/s41598-022-26586-0
AR #115
Dawn of the Dolphins
by Patrick Marsolek
