I am not sure if this was intentional, but I am at the point in the game where the birds blot out the trees, and the tab on chrome is seriously lagging. This is a picture of the game at that point.
It's intentional. But it was designed as a game over thing after everything else has been completed, so the user can crash out before leaving. The problem is one of balancing, it is too easy to get to the final bird level. You seem to have got most of the upgrades though, so you're as good as finished. As long as you enjoyed the journey, might as well blow up the destination. :)