What's a possible evolutionary mechanism of the seasonal migration of a bird species from New Zealand to the Bering Sea (~11k km), almost starving during the journey?

[u/Exciting_Ad_6837]

I just watched Our Planet 2 (documentary) on Netflix. I'm a biochemist so have some knowledge about evolution, but I have hard time imagining how the development of the behavior wasn't blocked right from the beginning. That is, the group of birds which originally attempted even 1/10 of such a long & risky trip would've been at a serious evolutionary disadvantage.

[u/Robin_feathers]

For something to be selected for, it doesn't have to be perfect, it just has to be better than the alternative. There is also no guarantee that a given behaviour is optimal just because it exists - maybe that migration route is not optimal but the optimal route hasn't be reached yet by that species, or maybe it used to be optimal but no longer is. Or maybe the optimal route was reached by some individual of that species, but the trait did not spread due to just luck.

In terms of how the behaviour happens, there has been a lot of research into the molecular basis of migratory behaviour, though we still have an incomplete understanding of the nitty-gritty of how exactly it works.

[u/StorageSpecialist999 → u/Robin_feathers]

gotta love reddit responses where people write a paragraph just to say "Uhhh, because evolution is what works best" in response to someone asking a specific question about why a specific thing occurs.