In the wake of building evidence that birds can see the planet's geomagnetic magnetic field, and how crucial this may be to their navigation during migration, a new study has found that disturbances to this magnetic field could be a significant cause of vagrancy.
The research, published in Scientific Reports, analysed 2.2 million bird ringing records relating to birds of 152 species captured and released between 1960 and 2019. This revealed a relationship between unusual bird movements and disturbances in Earth's geomagnetic field.
Ringing records were analysed to investigate the relationship between events in Earth's magnetic field and the occurrence of vagrants such as this Siberian Accentor in Highland in 2016 (Dave Tanner).
Morgan Tingley, associate professor at the University of California and co-author of the study, said the such magnetic disturbances would lead to the birds interpreting "distorted maps", potentially landing them a long way from their typical range. The planet's geomagnetic field runs between the poles and is influenced by a range of factors originating from within Earth and from space.
Vagrancy is usually a 'dead end' for birds. Once in the wrong part of the world, they usually either quickly die or live out their days in the wrong part of the world without breeding. However, vagrancy can play an important role in the rare cases when two or more 'lost' birds meet and breed in a new region, potentially expanding the species range or even starting a new evolutionary path.
The role of magnetic fields has only been the subject of more intense discussion relatively recently, with more established vagrancy theories including the effect of weather and the idea that young, inexperienced birds may head in an erroneous 'reverse' direction.
It was found that magnetic disturbances impacted both young and adult birds, suggesting that such events may have an impact on navigation regardless of the number of migration miles clocked up over a bird's lifetime. Correlation between magnetic disturbances and the discovery of vagrant birds was especially noticeable during autumn migration, while it was shown that disturbances caused by solar activity had a relatively minor effect on vagrancy. The researchers suggested this may be because radiofrequency caused by solar flares and sunspots would render the magnetorecepters in birds temporarily disabled, forcing them to use other navigational cues such as day length, topography and the night sky.
Reference
Tonelli, B A, Youngflesh C, & Tingley, M W. 2023. Geomagnetic disturbance associated with increased vagrancy in migratory landbirds. Scientific Reports 13.1 (2023): 414. DOI: https://doi.org/10.1038/s41598-022-26586-0
