I found this great resource that discusses the safety of common foods, woods and plants for birds.
Browse the table of contents for information (based on research) about the safety or potential risks for parrots for various types of plants, foods, wood, household items and anything that a bird in captivity could come into contact with.
Unless the evidence is clear, such as the case with avocado and chocolate (amongst several others), information is presented based on the research and expert opinions available. Many things are controversial when it comes to their safety or hazard potential for parrots, but often there is little evidence or knowledge either way, leaving it up to caring parrot owners to make sensible and considered decisions. In cases where the suitability or potential hazards are debatable, this is stated and wherever possible, links provided to expert opinion (preferably veterinarian or scientific studies).
There are hundreds of factors that can cause something to be dangerous to a bird (consider: quantity, quality, the bird’s general health, the parrot species; just to name a few), and there is rarely a black and white “100% safe or not safe” answer besides in cases that are well known amongst parrot owners (and clearly also stated in this article).
Sticking by the golden rule of “if in doubt, don’t” can give people peace of mind that they are providing the best for their birds, without unnecessary risk.