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> They use tail wind and thermals to cross large water areas:
> 
> https://phys.org/news/2021-09-migrating-birds-routes-uplift-conditions.html
> 
> "...recent advances in GPS tracking technology have overturned that assumption. Data obtained by attaching small tracking devices on wild birds has shown that many land birds fly for hundreds or even thousands of kilometers over the open seas and oceans as a regular part of their migration.
> 
> ***
> 
> "The findings not only confirm the role of tailwind in facilitating sea-crossing behavior, but also reveal the widespread use of uplift for saving energy during these nonstop flights. Suitable uplift means less drag, making sea crossing less energetically demanding.
> 
> "'Until recently, uplift was assumed to be weak or absent over the sea surface. We show that is not the case," says first author Elham Nourani, a DAAD PRIME postdoctoral fellow at the Department of Biology at the University of Konstanz, who did the work when she was at the Max Planck Institute of Animal Behavior.
> 
> "'Instead, we find that migratory birds adjust their flight routes to benefit from the best wind and uplift conditions when they fly over the sea. This helps them sustain flight for hundreds of kilometers," says Nourani.
> 
> "The oriental honey buzzard, for example, flies 700 kilometers over the East China Sea during its annual migration from Japan to southeast Asia. The roughly 18-hour nonstop sea crossing is conducted in autumn when the air movement conditions are optimal. "By making use of uplift, these birds can soar up to one kilometer above the sea surface," says Nourani."
> 
> Comment: Of course the birds would choose to do these methods as they must recognize the convenience. The real question is how did they develop the instinct of specific migration when long flights over open water is inherently so dangerous.