This may not be the exact interaction you were expecting, but maybe it qualifies. I do have shots of mom feeding this nestling and the nestling sticking its head out. What mom doesn't know is that when she was gone, her kid stuck its head out a little too far and lunged itself right out the hole... and impaled itself right on the very spines that are supposed to be protecting it! After hanging by a nail, stuck to the cactus, and screaming in agony for a brief time, the little bird fell 15 feet and crashed on the ground. Luckily, I was shooting from a ladder. So I climbed down and checked out the bird. It seemed to be okay, so I moved the ladder over to the saguaro to see if I could somehow reach the cavity. Finding I was able to, I got the bird and put it back in its hole. I moved out of the way and a few minutes later mom came back and fed the baby another meal. If she only knew what her kid was up to while she was away! This was yesterday. Had I not been there to photograph, this bird would have died. I went back today and the nestling appears to be doing well - calling like crazy from the cavity and eating every meal mom and dad bring.
Thanks guys! Ofer, it sure looks like blood on the cactus next to the wing. But this nestling wasn't bleeding anywhere that I could see. And the blood looked dry, so maybe it was from another bird. Maybe one of the parents or perhaps a sibling. From what I can tell, there is only this one nestling, so who knows what happened to the others.