blockage

I am wondering if anybody has seen this syptom and what might cause it. Pigeon stretches neck way out and shakes neck like when feeding a baby. Pigeon appears to be trying to clear a blockage but nothing comes out. Crop is empty.

I found a squeaker (Union Square) whose vent was damaged by an injury. We saw Dr Pilny (VIMAS) twice and things were moving along but since this morning the small opening to the side of his vent through which waste was passing through has closed down. I tube fed him early this morning the...