Footage of birds isn't going to carry any weight.
Footage of birds there that day in the way AND requiring a bank angle of at least 62 degrees to scare them away, along with whatever extreme attitudes occurred may help, but if they would have been scared away by a cautious approach of say 10 knots, his justification falls away.
Same applies if prudent action by the operator in response to constant birds was a mustering horn.
Sunfish makes a good point about real evidence.