Ellamumu, what E.S. wrote is absolutely spot on.
I would add:
sit extra super still while the familiarisation process is underway. Have all the Yummies in pre-chopped chunks. Hold them in one hand. Learn to flick each little bit with your thumb, the way you flick a marble. This reduces movement to almost nothing, and it’s movement that alarms the chicks more than anything.
Also, keeping yourself actually physically low is good too. If I am trying to hand-feed a non-tame bird, I lie on the ground, hat on face, perfectly still, with Yummies in outstretched hand, for as long as it takes.
The closer you are to the ground, the less of a threat you represent (‘cause the bird knows it can get away while you are rising. That's why even tame birds just won't sit in the presence of a human. They know that they are at a disadvantage).
S.E.
P.s.: gee, it's cool that you can check your birds for ticks. I dearly wish that I could!