Another vote to eating with your bird... I had the same nightmare when my bare eye too came home about 3 years of age. She had never seen fresh foods, and would not touch anything in the cage. But, I started bringing her to the table and it became a game of her 'stealing' food. So, became the norm that I would have a pile of Ivory food on my plate for her to 'steal', she loved eating what she thought all of us were eating and she quickly found her favorites.
Do your tiels enjoy shredding things? Hanging large pieces of greens in the cage as a 'toy' to shred. We do this all the time at the shelter for the large walk in aviary with the budgies and tiels, we have full pieces of different greens - kale, collards, romaine, chard, etc. The birds shred and eat, so its kinda like a game!
Another thing you can do is whatever the favorite treat or food, mix it in. Start with the simple stuff that most birds love like cooked mashed yams / sweet potatoes. Sprinkle some seed on top. Then once they are eating that, add another new item like pieces of green peppers. With smaller birds, a fine chop in the bird might work better. And add cooked rice or lentils in too. Along tho lines, a great intro to fresh foods that works with a lot of birds of all sizes are sprouts. Start with the easy stuff like regular lentils (tan color, not red ones, they tend to mush). When the sprouts are about half inch long, offer to your birds. And these are something you can share with your birds, if you like veggies and such, you might find lentil sprouts are a delicious treat. Around our house, my daughter and I eat as much for lentil and chick pea (garbanzo) sprouts as the birds do!!
And just keep trying... that's the other key, don't give up
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