Birds love to play with their food and if it available in excess or an amount that the birds can both eat and play with the food it may be very difficult a behavior to curtail. In some instances you may simply be able to cut back the amount fed and the bird will stop wasting.
Some birds may need to be “trained” not to waste by being given nuggets one at a time for a period or fed in small, distinct meals, with a few hours between feedings..
In some cases, ie sick birds etc. it may be best to let them waste until a later time as to when they are healthy enough to make adjustments as such.
Never starve a bird.