A study done on macaws and grays that showed that they would rather wait for a better treat instead of just taking the so-so one BUT, with all due respect to the scientists, there is no real comparison between a sunflower seed, a walnut and a lousy dry corn kernel. I mean, OF COURSE! they were going to wait for the walnut! Now, if they had done, say, a walnut, a pistachio and an peanut in the shell...
https://www.newscientist.com/article/21 ... t-walnuts/