I have a chick about 3 weeks old. Just moved them out of the brooder into an area where I can sit and watch them better. This chick has a strange buldge under its leg. It looks like an air bubble the size of my thumb. When the chick breaths in, the air bubble fill up and then goes flat when the chick breaths out. I know I will probably have to put the chick down but was just wondering if anyone has seen anything like this before. Thanks for any help or comments.