I'm sorry I haven't been able to reply sooner. The second time we tried to drain the mass under Reba's vent, the same thing happened - just a few droplets of blood in the syringe. Not even any air was released. I'm stumped. We waited for the worst of the summer heat to pass and then moved her back outside with her friends. She is back to free-ranging and certainly acts like she feels fine, but the mass is still there. It appears to be the same size - no bigger yet. I found a vet willing to take a chicken, but the costs were just astronomical. I'm not ready to do that just yet, especially since she seems like she feels fine.
After doing a little research outside of backyard chickens, I was able to find a couple other people talking about a condition like this. Some said that their chickens have lived for years with the mass on their backside. I find this so bizarre! I guess if the mass where to stay the same size though, it could happen. I'm hoping that Reba will be like that and continue to live a happy life. If anyone does find out anything specific about what this is, I'd definitely appreciate an update on this thread if you can.
try looking at prices at a vet school or an aviary rescue place. It might be alot cheaper