Usually two syllable words are easier to teach or learn than a single syllable. In fact our cockatiels seem to learn simple phrases better than a single word. We have one that says Pretty bird, hi Baby, kiss kiss etc. Another that says Gimme a kiss, Pretty Bird, Whatcha doin', and Sweetie bird. I haven't had any in that will say just a single word by itself. In my opinion it seems to interest them more with more syllables.
As far as simple tunes they do of course learn whistling easier than singing and ours will do the Wolf whistle, Jingle bells, and a few "chorus" tunes from newer artists. (In fact ours have a favorite right now a "Toybox" song called something like Best Friend that has a fast beat chorus sound in the middle. We have had mixed luck with Old McDonald. They do seem to like the quicker beats rather than the older slower beats to learn to whistle and actually do better with a "pop" type beat than the Childrens' songs beat.
Hope that helps
I don't think I noticed on the first question, how old is this cockatiel and is it definitely a male? If it is a normal grey or has been sexed of course it would be definite but we have had a few "males" turn out to be females and a few "females" turn out to be males because their markings looked more to be the opposite sex. And of course females won't talk and very rarely learn to whistle (in fact I have never seen one learn but have heard a few say they will whistle a little).
