hello,
I've played your game. First of all I would like to describe problems from my point of view .
1) Tutorial. it is hard to understand what to do . I would suggest to add some animation that shows what to do . For example, it can be a finger that taps on screen and provides a bird through obstacles. then player should continue providing a bird.
2) It is quite hard at the beginning. Together with poor tutorial it frustrates.
3) advertisement. banner on the bottom of the screen is okay. ( maybe it annoys on devices with small screens. it would be good to check). But advertisement after fault very annoys . When you are frustrated with a lose, forced watching of advertisement very distresses. first of all I would suggest to create a small animation of bird before lose. Then show a window with information "You lose :( Try again " and a button " replay" and clicking on that button shows advertisement. Actually, it would be better to create a charge, that decrease with replaying and increase with time or with watching advertisement.
3) coins (small birds that user should collect) .There are problems with their allocation . some times they are very close to obsticale and it's not possible to collect them. some times they are very close to each over.
Also, do you have some integrated analytics SDK in your game? it would be very useful to know how long users play , when they quit a game and so on . it'd help to understand problems of the game. Also, it would show how long users spends time with your game and how much times they lose , etc. that would give you understanding of the balance of showing advertisement.
Hope my remarks will help you. If you'll want to continue a discussion , I'll think on over ideas .
Sorry for mistakes, this text was written from mobile device.