Avoiding birds
If birds could read I'm sure the ANO would say birds give way to everything else. Just as a balloon does not avoid your warrior, you do not avoid birds.
You only have to watch a bird flying through trees and landing on a branch to realise they are far more agile in the air than your aircraft. If you have done all you can to be seen and heard, it's then their responsibility.
For all their skills, birds can be seriously irresponsible aviators - especially when flying in groups. You don't realy want to be sharing the air with them if you can avoid it.
Whilst they tend to come off second best in a collision, even if your aircraft is undamaged you do not get off scot free. If one hits you, you have to report it.
But since they are unregistered, you only need to report its type.