My duck has a swelling on each foot.

[canada-goose]

I was checking his feet today because he stands on one leg a lot and I noticed a pinkish swelling on each foot....in the same place. I don't think this is normal. He is an otherwise healthy Mallard duck. Please tell me if this is normal and (if not) how to cure it. I don't want him to be lame for life. Thank you!