Vocal expressiveness 
Loudness 
Ability to speak human language 
Ability to learn tricks 

Cockatiels are smaller in size as compared to other parrots. They like to be petted and are satisfied as long as they are near you. They are smart, enjoy learning new tricks and like to be rewarded for good behavior. 

Not every cockatiel will learn to talk, but they are best at imitating other birds. Also, to prevent your cockatiel from feeling depressed, it’s best to get them a companion.