Interesting question Katybird... I actually plan to write on that topic, however I am a firm believe that those differences have a lot more to do with the exact way the bird was raised, fledged, weaned, ad socialized rather than species

of course that is a pretty hot topic.
A few of the things I would like to know more about are
-things that can go wrong inside the egg, how to prevent them, how to identify them, and how to treat them.
-Differences in how different species respond to the same types of training (such as the specifics of how my pionus was traumatized by being treated like a cockatoo by a self proclaimed cockatoo expert)
-The role of genetics in temperament
-the role of early nutrition in overall health as an adult, and if there are any links to temperament
-hard numbers on the health and lifespan of flighted vs. clipped birds
-More specific nutritional breakdowns by species, age, activity level, climate, and more.