How Do Animals Adapt To Dry Climate?

If they are giraffes according to ETheory, they grow longer necks and eat from tops of trees.
Sounds alittle dumb/stupid to normal thinkers. Why didn't they just walk to a better eating place?
That's what other grass eating animals do. Called migrating, or perhaps there are more long neck animals we haven't seen.

They can adopt by their body type and living preferences.