Thank you very much for your comment :)
It took me at least two days to finish the backgrounds, but I'm quite proud of the result. I even managed to create simple animations with the “Tiled Background” object.
The main mechanics weren't that complicated to set up. You just need to give the chickens a little push upwards and to one side when an area of the screen is touched (with a certain speed threshold that mustn't be exceeded so that the chickens don't go too fast). For the rest, if all objects have physical behavior, then all objects interact with each other naturally (and chaotically too ^^).
However, this was the first time I had used physics to this extent in a game, so I would be lying if I said I didn't struggle with how certain objects worked.
I also made a beginner's mistake by not taking delta time into account when managing the chickens and propellers, which means that depending on the FPS and/or refresh rate of your screen, the physics may behave differently. This may explain why you found it a little slow. Because, sure, these chickens aren't speed demons, but they don't seem that slow to me either... (at least I don't think so).