I have seen this, it's so very sad. I live in south-east Queensland where this phenomenon does occur, it seems to be worst at this time of year. The best guesses are that it may be an introduced species of summer flowering plant that rainbows are eating that they shouldn't be, or some kind of bacterial infection or even a pesticide. I've never personally encountered a paralysed lorikeet but it does make me rather paranoid when it comes to giving flowers to my lorikeet, Lovejoy. I always stick to the native stuff and try to grow my own so I know it hasn't been sprayed, but since the cause is unknown and may even be spread by the wild ones visiting my garden, I have to wonder sometimes if it's worth the risk 😟
