The subtle differences in plumage of even our most common birds are always good to puzzle over.
The two sets of images below illustrate this.
First off, the Fuscous Honeyeater. The first individual shows barely a trace of a plume, while the bill is dark, not black, suggesting this is an immature bird from spring breeding.
In the second image the yellow plume with a small black patch is much more obvious, while the base of the bill and gape are yellow – an adult in non-breeding plumage. Breeding adults are almost identical, except the bill and gape are deep black. The eye-ring is yellow in the adult, but pale in the immature, however, this feature can be variable in my experience.
The Eastern Rosellas also present a challenge. The individual at front is, I suspect, an immature – the pale yellow and green plumage on the nape and crown a feature of younger birds. It is accompanied by one of its parents, I think the female, going by the less than vibrant red on the head and slightly off-white cheek patch.