First, they don't land in the exact same place[s] every year.<quoted text>
A couple of weeks ago the ducks started migrating through Illinois. They fly in that “V” formation and you can hear them honking. Hundreds flew over the homestead.
Scientist say they save a lot of energy flying in the “V” formation versus flying alone. They’re able to navigate without a compass and GPS. Landing in the exact same place every year.
Some of the smaller birds fly all the way to South America. Pretty amazing stuff.
Second, that's a very simple and well understood phenomenon. Birds that don't fly to warmer locales die off, without being able to breed, so only those with the genetic trait that makes them fly to warmer locales spread their genetic traits, because birds are inherently unable to maintain body temperature in colder environments, they cannot survive well.