G’day Nikolas,
Raja’s photos of the juv Salvin’s from Wollongong june last year, on this side of the Tasman, is the most useful set you should be looking at in that link. EG., note how dark the bill is, darker than an adult as you would expect. The Sydney bird in question from this year has a bill that is paler than an adult Salvin’s. Does anyone out there have photos of definite juvenile Chatham’s.
Cheers Jeff.