Refined sugar isn't acutely toxic, but it has no place in a parrot's diet — it crowds out nutrition and contributes to obesity and other health problems. Avoid added sugar.
Keeper's noteThe practical takeaway: avoid sugary human foods and 'treat' products. Natural sweetness from fruit is the right way to give your bird something sweet.
What to watch out for with sugar
Parrots get all the sugar they need from fruit, which comes packaged with fiber and vitamins. Refined, added sugar is empty calories that promote obesity, fatty liver disease, and an imbalanced diet. It isn't a poison like chocolate, but there's no amount that benefits a bird.
How to serve it
Avoid added/refined sugar entirely.
Get sweetness from whole fruit instead.
Watch for hidden sugar in cereals, sauces, and bird 'treat' sticks.