It's just a normal thing, nothing bad. I have 5 Budgies and that happens to them all. They just change as they get older, I only have one that doesn't for some reason and she is a female

Edit: Only happens to males

I own two healthy budgies. I've noticed their black nails...Why's that? I feed them everyday and clean their water everyday too. Is it an infection? Both of them have it. I'm so confused. I've had them for a month and they're pretty well tamed