If you are offering other food for Powder to try (fruit, veg and seed etc), then he may be trying those and begining to wean himself. I found that around the age of 6 weeks my babies started to take less formula.
I would keep trying to give formula as well as offer fruit /veg etc.
They do need to drop weight in the wild so they can take flight eventually so I believe this is what Powder is going through, his natural instinct.
