Sorry to hear about the chooks. Congrats on the baby! Honestly, though, my bet on the chook is abcess. I had a hamster who had an abcess under her arm. We thought that it was a huge tumor (so did the vet), so we were just going to let her live until she seemed bothered by it. It then started scabbing up, and the scab grew and grew until one day it just oozed out. She had the lump for a long time too.