I agree with Ted! Make the bird WIDER by feeding it more! Here is some pseudocode to help you achieve that:
I haven't tested this code but I'm pretty sure it would work.
Maybe you could do something progressive, like make the background change colour every 10 food you feed the bird, to do that you need to make a skybox material and access the material's colour through the code, and then on your bird feed code, you need to check if the bird fed amount is a multiple of say, 10 for example. and if it is, you simply need to tween the colour value from the current to the next, you can use an array of color32 for this.
