A new paper by Dr. Jeremy Ross from the University of Oklahoma describes the use of tiny devices strapped to birds' backs called geolocators, which capture the individual migration routes of lark sparrows in North America. By sensing the light levels, these backpacks can pinpoint the location of a bird anywhere in the world, even if retrieving the data-logger can sometimes pose a major problem.
This study, published in the online journal Animal Migration, mapped for the first time the routes traveled by three lark sparrows after they left their breeding grounds in Ohio. When the birds returned to the site the following year, Dr. Ross and colleagues retrieved their loggers and mapped where they had gone in the interim. The results of this work, which represents the most detailed tracking of this species' migration route, showed some surprising findings. While the three birds all appeared to have spent the winter in Central Mexico, they each took different routes to get there, and there were differences in their overall pace as well. One bird made a beeline to the destination, while another took a more scenic route along the Gulf coast. The third bird took its time and wandered through the central region of the United States before finally making its way to Mexico. The authors believe this bird did so because it needed time to molt its flight feathers.
According to Dr. Sidney Gauthreaux, a leading expert in avian migration, "within the last few years the use of geolocators on small birds has grown exponentially, and many studies are underway. Unlike bird banding where only banding site and recovery site are generally recorded, a researcher can use a geolocator to record the day-to-day movements of a migrating bird. This technology is currently the best way to track small birds for extended periods of time."
Other findings from this study showed clear differences in migration timing between spring and fall migrations, as well as the locations of important stopover habitats along the flyways.
"Studies like this one are greatly improving our understanding of avian migration, and they are a welcome contribution to this journal." said Dr. Andy Davis, Journal Editor of Animal Migration.
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The article is available fully open access on De Gruyter Online.