Birds can be afraid of smaller things... so I'm half wondering if Weeble and Beeper were afraid of Bongo at first...
I have had small birds and large birds together... both unintentionally and intentionally.
Smurf, the budgie, would crawl between the bottom bars of the cage and the tray itself to go hang out in Noel, the conures, cage. I freaked out at first when I saw this occur, but later realized that they pretty much kept to themselves! I assumed Smurf did this as a way to escape from the girls (other budgies), since they weren't always so nice to him! And whenever I caught him in the act, he'd always make his escape out of the cage!
Then I converted a bedroom into a cage-free bird-room and was able to have everyone get along.....
Then Charlie (conure) came along... and later Normie (budgie)... and that changed things! These are pictures right before I took Normie to her new home! Smurf had died (some farm illness I don't know how he got), leaving me with the girls, and since they were healthy, I rehomed them together. I had a pair of budgies that I never introduced to the rest of the budgie flock, and the male from that pair died (AGY... didn't find out until necropsy results... all previous tests didn't detect it
), which left me with a lone hen.... Normie. Well, whenever I let Normie out of her cage, she took it upon herself to squeeze between the bars of Charlie's cage and play with his toys and eat his food. This infuriated Charlie to no end! As amusing as it was to watch Charlie lumber around his cage chasing her, and she nimbly avoiding him, I knew it was a dangerous situation! After I boarded my entire flock, her behavior became even worse, and so I found a budgie only home for her!
Ever since, I have not had such a large difference in size of species living together. I mean, I have had my bourke (prior to her passing) living with my cockatiels for a short while, but she did best alone. (she was happier living with the cockatiels, but then she'd get sick.... kept her separate and cared for her separately, she was healthier....) Right now, I do have an ARN with my cockatiels, but weight wise, she's not much bigger. Body wise though, she is quite a bit bigger! Although the ARN isn't friendly with the tiels, they get along. I wouldn't try this in a smaller space though, as that would probably be trouble!