I do feed cheese and other diary products, such as yogurt, cottage cheese, string cheese, etc., and all my parrots seem to enjoy the weekly diary treat.
I've discussed this with our Holistic Avian Veterinarian and our main Veterinarian who is a Professor, both agree--small amounts are helpful not hurtful, although parrots don't seem to have the right enzymes to break all of the components down. It is still a nutritious treat, and I've (knock on wood) never seen any discomfort in our flock.
So, I was encouraged to feed diary products
My flock also gets a large amount of egg (hard boiled with shell) since we have our own layers. I mix about 6 HB eggs in with 2 cups of rice and serve warm.
You also need to consider the phosphorus ratio for absorption for the foods you feed. I made the mistake when researching food items to feed for calcium and didn't consider the phosphorus ratio in that particular item. The best calcium absorption ratio is 1: 0.5
There are many other excellent calcium food items to choose from, such as turnip greens, cabbage leaves, dandelion greens (1: 0.4), broccoli stems and leaves, kale (1: 0.4), spinach (1: 0.6), oranges (1: 0.4),
Moderate Calcium sources include
Strawberries, blueberries, squashes, turnips, orka, carrots (1: 0.9), cantaloupe, green beans (1:1), black berries, etc.
Poor calcium sources include
Apricots, plums, cherries, cauliflower, grapes, peaches, corn (which is one of the highest items I feed is 1: 12.9), bananas, pineapple, asparagus (1: 2.5), pumpkin, cucumber, etc. These food items are helpful in many other areas and safe to feed--but they are not a good choice of calcium.
Vitamin D sources safe for parrots would be, diary products and eggs, dandelion greens, egg yolks, oatmeal, sweet potato, alfalfa and parsley. "Vitamin D is fat-soluble and has properties of both a vitamin and a hormone, is required for the absorption and utilization of calcium and phosphorus". Feeding cheese once a week I believe is good for your parrot. A parrot that is already on a balanced, nutritious diet consisting of fresh foods, sprouts, breads, seeds, nuts, and mashes....not any one item is considered "complete", it is a combination of many nutrients that give your parrot ultimate health.
Our parrots are extremely healthy, with beautiful feather, bright eyes, excellent color in plumage. Our hens are tested for calcium, because I don't believe all breeders should be automatically supplemented. Even on the hen that produced the most babies and eggs in a 12 month span has a good calcium level when tested. If you suspect the diet your birds are presently on is lacking you can have a Blood Chemistry Profile done, to see where your birds are at. And what I find is parrots will balance their own diet, but it's up to you to offer a good selection