I have all the three other "fuels" for the phone, I released the bird, and I smashed the window in Winter.

I looked it up in a walkthrough, and supposedly the bird should show up in Winter with a blossom, which I can then put into the mixer for the final fuel.

But it doesn't - it just sits there out in the tree. What am I missing?

I played this on my phone, I'll try to refresh my memory.
Have you tried travelling to a different time/season?
You should find the seed, the bird and then the bird ehm in a different state, in different seasons.

I think it needs his music to be played to get attracted.