Here's a study on cockatiels' sense of taste, where they experimented with giving the birds a choice between plain water and water that was sweet, sour or salty:
http://citeseerx.ist.psu.edu/viewdoc/do ... 1&type=pdfThe sweetness had to be fairly intense before the birds acted like they even noticed the difference, and when they did notice the difference they rejected the sweet water in favor of the plain water. The way they perceive sweetness is probably different than the way we do, and they don't seem to like it. Which is one reason for them to not like fruit.