ABSTRACT
Advances in tracking technologies have revealed the diverse migration patterns of birds, which are critical for range mapping and population estimation. While population trends are typically estimated in breeding ranges where birds remain stationary, trends are commonly assessed in non-breeding ranges for species that breed in inaccessible regions such as the Arctic. This task is challenging due to the extensive movements of birds in these ranges, which require a deep understanding of the dynamics of these movements. However, these movements remain understudied, particularly in the mid-latitudes, where many Arctic breeders winter, increasing the risk of misestimating their ranges and numbers. Here, we show that the Arctic breeding raptor Rough-legged buzzard, which overwinters in the mid-latitudes, has a specific wintering strategy: during the entire non-breeding season, they move about 1000 km back and forth under the influence of the advancing snowline, making their non-breeding area dynamic. In essence, this movement represents an extension of the quick migration process, albeit at a slower pace, and we have termed this migration pattern ‘foxtrot migration,’ drawing an analogy to the alternating fast and slow movements of the foxtrot dance. These results highlight the potential errors in range mapping from single mid-winter surveys and emphasize the importance of this migration pattern in assessing the conservation status of bird species. Understanding this migration pattern helps to correctly estimate bird populations in non-breeding areas, which is especially important for species that nest in hard-to-reach regions such as the Arctic.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
We have completely rewritten this substantially revised manuscript's Introduction and Discussion sections. At the reviewer's request, we have removed the overly long paragraph on basics at the beginning of the Introduction and all references to foxtrot migrations from the Introduction. In the Discussion, we have added a substantial section (and made it the first) on how the pattern we describe differs from itinerancy. We also revised Figure 4 to show this difference. Regardless of the terms, itinerancy and the pattern we describe are two different behavior patterns with distinct biology, dynamics, modes of origin, and geography. We have shown that in our case, unlike itinerancy, birds do not stop for 1-2 months at 3-4 non-breeding sites but migrate considerable distances - 1000 km - throughout the winter. Also, unlike itinerancy, in our case, the sites where the birds arrive are free of snow throughout the year, i.e., if we follow the logic of the publications on Montagu's harriers to which the reviewer refers, the birds do not wait for favorable conditions at the next site, as happens in itinerancy. Also, unlike itinerancy, it occurs under the influence of external factors - snow cover dynamics and in mid-latitudes. Moreover, researchers who observed a similar pattern while studying a species close to our object - the common buzzard, did not use the term itinerancy but used the term - 'prolonged autumn migration.' In their studies, the transmitters stopped working in the middle of winter, and they did not see the whole annual cycle. Still, they caught the general meaning and tried to convey it - it is precisely continuing migration, but at a slower pace, which is not similar to itinerancy. Overall, we believe that the manuscript has been greatly improved. We are grateful for the reviewers' constructive input and appreciate the opportunity to incorporate their comments.
