The bigger female falcon tended to be the one swooping down and attacking, he said.
Birch, who snapped a photo of the falcon swooping, mid-attack, on his friend Steve Millar, said he too had been hit by the birds.
"They tend to be swooping and their talons are just hitting the biker's helmet to let them know they shouldn't be there."
He said it happened fast and was quite an aggressive swoop with a bit of a bang.
Birch said he had been using the trail in the last 10 days but had now decided to avoid the trail and take the road around.
He said hundreds of people used the trail and thought it should be closed for the public's safety and to give the falcons some space.
"A lot of mountain bikers I've spoken to think it's a bit of a laugh, but we also think they should close the trail, and people should go along State Highway 5 and detour."
Birch said there were signs up saying not to walk dogs through the area, "because the falcons would really have a go at dogs".