Photo helps ID this bird

An immature red capped parrot, taken near Dunsborough, WA

Sometimes a photo helps identify a bird.  My first impression of this was that it was an immature red-capped parrot, but then I noticed it was with a group of Western rosellas, so I wondered. Luckily I managed to take this (very poor) photo before it flew off. The extra long bill, long tail and other markings match the illustration of an immature RCP in my Slater's Field Guide.