What changes the food answer
Use nuts like a reward, not a staple. The right amount depends on species, size, activity, weight, and the rest of the diet.
Choose safe nuts
Offer plain unsalted nuts in bird-sized pieces. Avoid salt, sugar, flavor coatings, chocolate, rancid smell, mold, and shells that may be unsafe or dirty.
Use them for work
Tiny nut pieces can make training, carrier practice, stationing, and foraging more rewarding without filling the whole bowl.
Adjust for the bird
Macaws may handle nuts differently from budgies, Amazons, cockatiels, or overweight parrots. A tiny bird needs tiny rewards.
Best rule
The more exciting the treat, the smaller and more purposeful the portion should be.