About a week ago, my muscovy drake (just shy of six months) developed a very strange mass on his breast. It is very disproportionate to his body, and is enlarged toward the right side. I have felt it, and it feels hollow and flexible, which is why I left it for a week hoping that it would clear up. It hasn't gotten better, but it hasn't gotten worse. He walks around normally, and appears to be eating and drinking normally (I feed scratch every morning and night, and he has definitely eaten that as well as pellets.) I have never seen this in my flock before, so I don't it's genetic (but his mother was also the mother of the drake that sired him). He has access to fresh food and water on a daily basis, and I don't think he has sour or compacted gizzard (do ducks get this?) I don't believe that there is anything harmful in my yard, but stuff from the previous owners of the house tends to get kicked up from the dirt (such as wires and nails, which are normally taken care of by me as soon as they pop up). Should I just monitor it or do I need to take a more hands on approach? I would rather not loose him since I'm planning on selling him in a trio later this year.