What beak size became an adaptation after a drought left mostly plants

with large, tough seeds?

their beaks became tougher as well. and example of this id a toucan

After the drought, the medium ground finches that managed to survive had smaller beaks than those that had perished, probably because they were better suited to eating the small seeds that their competitors avoided ... This genetic shift is likely responsible for some of the reduction in beak size, the researchers say.