Aargh! What bird is eating my scarlet hawthorn flowers?

[wildstrawberryplace]

I planted a young Paul's Scarlet may tree last year and was pleased to see masses of buds for flowers this spring. I did notice a collared dove eating the green buds so I shoed it away a few times.

Now it has flowered, but the flowers are diminishing by the day and if you look closely you can see hundreds of stalks where there should be flowers.

Something is eating the flowers - but what? The collared dove again? Or maybe a blackbird? How can I stop it?