Evidence.

Showing the neighbour's ladder next to the fence which he pulled out right next to the tree which had a nest in it, two days after I'd told them there was a bird nesting in it and that it was an offence to disturb it.

The neighbour wants me to reduce the height of the tree but when I had someone out to do it the guy showed me a bird on a nest and couldn't do the job.

In the process of painting / creosoting their fence they have damaged mine which are next to each other as I don't trust them as I've seen them lift these panels and walk into other people's gardens to get balls back without asking.

I've told them that I will not do the tree until November now to ensure all other birds remain undisturbed.
Reported them to the RSPB who wanted me to phone the Police's Wildlife Officer as it is a crime to disturb a nest which is being used or being built. I don't trust the neighbour not to retaliate but I'd love to know if I really have to do anything about the height of this tree now, especially after him damaging my fence which is going to cost me to replace.
I'm not asking him for the money as I hate confrontation and just know he'd refuse. They tell such bare faced lies that they'd say anything, that it fell down by itself and it was just coincidental that it was fine days before and badly damaged after he'd pulled out his fence panel.

I know he was trying to disturb the bird so the tree could be done.