try elevating the feeders 4-5 inches above the floor of the cage so the birds have to reach up into the feeder to get food. This should eliminate most waste.
You should always feed poultry and fowl freely. They will not overeat to the point of causing themselves health issues as long as they are only getting the proper food plus what they're foraging, and not extra treats. Typically when you feel like you're burning through feed it's due to waste at...