Am I the only one who finds this a little suspect? Why would their beak sizes reverse so quickly? First of all, these birds have a much longer lifespan than the moths, so you wouldn't expect them to revert as quickly as the moths do.
Secondly, I wouldn't expect something as trivial as beak shape to so greatly impact the outlook of a species. With moths, you have a very clear selective advantage in camoflauge.
With beaks, you have a specialization, but change should occur slowly. Further, unless humans are destroying large swaths of habitat, the long-beaked birds should still have a survival advantage for their selected niche because they are best suited towards that food source (even if the other birds are best suited towards human habitation).
It is strange. Just wanted to see what everyone else thought about it.