It stands to reason that bad weather can occasionally cause birds to become disoriented during their annual fall migrations, resulting in them landing in unfamiliar territory. But why do birds travel far from their usual paths even when the weather isn't a major factor?
An explanation is examined in a new paper by UCLA ecologists: Even in perfect weather, especially during fall migration, disturbances to the Earth's magnetic field can lead birds astray—a phenomenon known as "vagrancy" by scientists. Scientific Reports has published the study.
Assessing the causes of vagrancy could help scientists better comprehend the threats faced by birds and the ways in which they adapt to those threats in light of the steady decline in bird populations across North America. For instance, birds that find themselves in uncharted territory run the risk of experiencing difficulties in locating suitable food and habitats, which could lead to their demise. By "accidentally" moving birds into areas that are now better suited to them, it could also be beneficial to birds whose traditional homes are becoming uninhabitable due to climate change.
Numerous factors, both above and below the planet's surface, generate the magnetic field that runs between the North and South Poles. Magneto receptors in the eyes of birds may be able to sense magnetic fields, according to decades of laboratory research. From an ecological point of view, the most recent UCLA study supports those findings.
Morgan Tingley, a UCLA associate professor of ecology and evolutionary biology and the paper's corresponding author, stated, "There's increasing evidence that birds can actually see geomagnetic fields." Birds can navigate by geography in familiar areas, but geomagnetism is easier to use in some situations.
However, when geomagnetic fields are disturbed, birds' ability to navigate can be affected. These disturbances can originate from a variety of sources, including the sun's magnetic field, particularly during times of increased solar activity like sunspots and solar flares.
According to Tingley, "it's like using a distorted map that sends the birds off course" when the geomagnetic field is disturbed.
Together with Tingley and postdoctoral researcher Casey Young flesh, lead researcher Benjamin Tonally, a doctoral student at UCLA, compared data from 2.2 million birds, representing 152 species, that had been captured and released as part of a United States Geological Survey tracking program between 1960 and 2019 with historical records of solar activity and geomagnetic disturbances.
The researchers discovered a strong correlation between the geomagnetic disturbances that occurred during both the fall and spring migrations of birds that were captured far outside their expected range, despite the fact that other factors, such as weather, probably play a larger role in causing vagrancy. However, the authors noted that the relationship was particularly pronounced during the migration in the fall.
Young and old birds were affected by geomagnetic disturbances in their navigation, indicating that birds rely on geomagnetism in similar ways regardless of their migration experience.
Geomagnetic disturbances associated with increased solar activity were anticipated to be associated with the greatest vagrancy, according to the researchers. They were surprised to learn that vagrancy actually decreased as a result of solar activity. The solar disturbances' radiofrequency activity may render the magneto receptors of birds inoperable, necessitating the use of alternative navigational cues.
Tonelli stated, "We believe that either a pause in migration or a switch to other cues during fall migration is caused by the combination of high solar activity and geomagnetic disturbance." Interestingly, this rule was rarely broken by day-migrating birds, who were more affected by solar activity.
Even though the researchers only looked at birds, their methods and findings may help scientists figure out why other migratory species, like whales, get lost or get stuck far from where they normally live.
Tingley stated, "We hope our work will assist other scientists who study animal navigation." This research was actually inspired by whale stranding.
Tonelli created a web-based tool that tracks geomagnetic conditions and predicts vagrancy in real time to make the research more accessible to birdwatchers. During the winter, the tracker is unavailable, but it will reopen in the spring, when migration resumes.
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