study of green parrokeets

recently on tv i saw a study  taking place of green parrokeets captured and kept in cages and the cages placed by feeding stands in gardens to see the effect they have on other birds coming into the garden to feed. I personally found the report made biased saying the other birds definately did not come near the feeders while the parrokeets were in the cage..i have many feeders in my garden and i also have a lot of parrokeets feeding from them but i can honestly say when they are feeding they do not deter the other little birds,  as i type this i have 2 parrokeets,  1 robin,4 sparrows, chaffinch, starlins, and they are ignoring the parrots...i do wish these silly studies would be more sensible...any creature captured in a cage will however deter and frighten others, all this type of study shows is how we are seeing ' a problem'...numbers of birds it seems are on the decline and it seems parrokeets are the number one enemy...i have many squirrels who constantly raid the nests and it annoys me...you dont see parrokeets robbing nests and i feel this is one of the major problems of decline in numbers...but as i said not in my garden!