Flappy Birds is copyrighted for .Gears under the creator Dong Nguyen. Even if you are not copying from Nintendo, you are definitely copying from Dong Nguyen. He owns the right to his program, just as everyone does when they create a game. Making a direct clone of a game goes against the rights of that developer.
Keep in mind, that when you create your own game, how you’d feel if someone was to steal your entire game and use it like their own. It is all about morals, values, and developer etiquette towards other developers.
I didn’t only talk about the tubes, ctomni231 is completely right, my very last sentence mentions Flappy Bird itself. egonolsen (the creator of the proprietary engine JPCT) talked to me here on JGO about Bern’s convention several years ago, I was plain wrong about copyrights and I read some important parts of this convention to understand what he meant. I advise you to do the same.
As the one who just derailed the topic, I ask you stop the nonsense on copyright, he is using it for personal use and isn’t doing harm to the creator by distributing it here, and by copyright law (of the US) no one can arrest him for that, now if he sells it, thats a different story. But still, respect the original creators rights.
I suggest you to read again the Title 17 of the United States Code paragraph 107. opiop65 is right about the amount of copies. Moreover, Fappy Bird is extremely (graphically) close to Flappy Bird. According to the factor 3 mentioned in the T. 17 USC § 107, there is no chance that this game can benefit of the fair use, that’s why I suggested GamerSucht to make substantial changes in his game.