I feed my Green cheeked conures once a week with a handful of sunflower seeds only when they are breeding, to give the chicks a little boost
An article written by a famous Australian aviculturalist by the name of Stan Sindel, he did a study with feeding on French White millet only as well with the addition of fruit and veggies, compared to feeding a mix of sunflower and other seeds. The results were astonishing and birds of the millet diet were living longer, healthier lives in collections of birds around the country- They don't call Stan Sindel the 'Father of modern Aviculture' for nothing!
Black cockatoos are an exception, with them requiring amounts of sunflower for their high fat diet, that they would normal obtain through their natural diet of pine and casuarina nuts
Thanks
Noah Till