A great simple idea, but could really use some better implementation at certain points. It's a good combination of genres that really fit well together.
Unfortunately the execution wasn't the best at times. The movement took a bit of time getting used to, as well as the physics as it doesn't quite feel as you expect it would. The transition is really sudden, and often the killing factor in the game which was disappointing to die that way. Sometimes the cats in the pigeon levels were invisible and I would die for no reason in them as well. They seem to only spawn at the top and bottom though so you could just keep the pigeon center and not worry about anything. I also managed to die as the pigeon, but then transitioned to a rat and carried on playing, managing to get 50seconds.
Overall, a great idea with the core idea implemented fairly well which could be a good mobile game idea with some improvements made.