This is a question that has been asked many times by the lovely people who believe in research before taking a sunny home!
Sun conure's as a rule, are not difficult to please! They thrive on a staple diet of good quality pellets, nuts, a few seeds and fresh fruit and vegetables.
The seed only diet should be far behind us but sadly, not. Most petshops stock seed and dried fruit mixes which are high in fat, low in nutrition and when it comes to the dried fruit(sulpher dioxides used in the process of drying are harmful) and peanuts - poisonous!
Vitamin's are very important for your birds health and most good quality pellets such as Harrison's, Zupreem or Kaytee provide much of the vit's and mineral's your sunny will need to stay healthy.
For example, Vitamin A is important to all birds as a deficiency of it can cause severe illness and even death. The deficiency causes malfunction in the respitory system most commonly. Vit A maintains the secretion of mucus and without it, your birds breathing can become laboured and clogged up. It can also affect the organs. This disease is commonly found in birds that are fed a poor quality all seed diet.
Vitamins B,C,D & E are also important for all round good health. A severe deficiency in any of these can result in rapid ill health but with todays knowledge, we know a good diet - especially of fresh fruit and veg - is very effective at ensuring this does not happen.
Sun conures especially need to have a good intake of Vit K which is not neccesarily needed for ALL parrot species. Vit K is known in simple terms as "natures warfarin". Sun conures (and some other members of the conure family such as patagonian, blue crown and nandays) are more prone to developing blood issues without this vital vitamin causing Conure Bleeding Syndrome. Luckily my own sunny enjoys the foods high in Vit K such as kale, broccoli, sprouts and spinich.
Dandelion is VERY good for your bird - high in Vit K and other essential Vit's - and can now be easily found pesticide free and dried in the rodent section of most pet shops. Other greens high in Vitamin K that can be fed daily are alfalfa, brussels sprouts, collards, mustard greens, turnip greens, asparagus, dandelion greens, endive, okra, peas, Basil, coriander, marjoram, oregano, sage, thyme, plums, prunes, soy bean and yogurt(careful with the amount, lactose intolerant and all that!).
If your bird shows a resistance to Vit K foods, one of the best methods I have found is to buy frozen spinich in the supermarket. This comes in handy single serving blocks which when defrosted and heated up, stick nicely to all the other veg your bird favours so he eats it whether he wants to or not!
Additionally, Vit D is thought to cause this disease in conures and we can ensure our birds stay healthy in this by adding the occasional piece of fish, eggs or even cod liver oil to their diet. The easiest and most healthy way to ensure your bird gets vit D lots of SUNSHINE! UV lamps can be used very effectively in the gloomy cold weather also.
All birds are different and what one bird loves, another bird hates! For example, my girl refuses to touch anything citrus. She also dislikes banana.
Getting to know what your bird likes will be trial and error. Don't be afraid to try new things, but be sure to research what NOT to give your parrot and check new foods are safe before offering it to your companion.
If I had a penny for everytime someone said: "But he likes chocolate" I would be rich! Chocolate can and will kill your bird if he is fed it regularly. Cocoa is poison to them and I would not risk so much as a lick. Dog's LOVE the taste of anti freeze....would you give a dog some just because it was "a small bit"?
Here is a good link to get you started of toxic foods.
Peanuts can be dangerous due to a natural fungus so personally, I avoid them altogether.
Instead my girl enjoys: pistachio, hazelnut, macademia and brazil. These are all raw and unsalted human grade.
Sunflower seeds ARE good for your bird despite some people seeing them as a no no. In excess, they cause weight gain but as a treat, they can provide Vit E and calcium to your bird.
Other seeds she enjoys are pumpkin & pine.
Nuts and seeds together should only ever be around 10% of your birds overall diet.
I always find it interesting that considering pet birds were fed seed only diets for many years, most will drop a seed in favour of a juicy piece of fruit any day!
This is the reason Cal's personal nut and seed list is so small....she simply threw away most of the varities I tried....big change considering she was fed one of those dreadful parrot mixes from when she was weaned until she came home with me!
Fruit and veg must be washed thoroughly. Whether it is raw or cooked is really down to the preference of your bird!
Fruit I have found success with are as follows.
grapes (no seeds please)
tomato (no green bits AT all....these are dangerous to your bird)
Veg I have found success with are...
kale (be careful not to feed this too often.)
Please remember that highly coloured fruit or veg can make your birds dropping vividly coloured!
I continue to try new things as they come into season. If I am in doubt of their safety I research! I generally feed my girl a small amount of fruit and veg (one in the morning, one in the evening) everyday in a seperate bowl to her pellets and nuts/seeds.
Ensure you mix up the diet, feed different things daily to keep it interesting. Try as best as you can to buy and try the seasonal fruit and veg. In the wild, your bird would eat as the season afforded. If you watch him carefully, you will probably find he favours some fresh foods over others at different times of the year. Respect this and try to make his menu as healthy and exciting as possible!
Some herbs and even flowers are very beneficial to your bird but unfortunately, being in the UK, I can rarely find flowers that I can be sure are organic.....I continue to research and be on the lookout!
Table foods can be popular as an occasional treat for your bird. Small pieces of grilled chicken, scrambled egg, boiled egg with some shell, plain and salt free crackers can be relished by some sunnies.
If it is good for you, chances are it is good for your bird.
EDIT: A very kindly gentlemen who kept all manner of smaller parrots and conure's in his younger years brought me a book to read that was his "birdie bible". This book is called Encyclopedia of Parakeets and was made in 1989.
It states that all conures and parakeets can have ALL their nutritional needs met with simply sunflower seeds, millet and canary seeds!!!! My goodness.....how times have changed. If this is not a reason to ensure you constantly research your parrots diet, then I do not know what is! So little was known about the subject that in the actual sun conure section, it states the bird you bring home will more than likely have come straight from their origins from near the equator, you must keep them at 20 degree's at all times! Cal would be begging for a bit of air!!! Apparently one of their "Downfalls" is they chew wood. Now we actively encourage this activity!!!
I have added this information to hammer home the point that seed only diets are very, very out of date and that it is our DUTY to give our companions the best diet we can!