Red-billed vs Silver Gulls

Subject: Red-billed vs Silver Gulls
From: "Rohan Clarke" <>
Date: Sun, 27 Jul 2003 15:21:28 +1000
Ross posted links to images that appear to show a typical silver gull and a typical red-billed gull (still both Larus novaehollandiae). They illustrate the presence or absence of a mirror on P8 nicely.
What I wrote was:
"There seems to be some OVERLAP but the differences can be summarised as GENERALLY..." (I've added the caps)
The reason I wrote this is no one character appears to be definitive (inc the presence or absence of a mirror in P8). For example I have copies of photographs taken in NZ by Brent Stephenson that show a putative adult Red-billed Gull (identified on range) with a very small white mirror on P8. What I would argue is that in combination the presence or absence of all characters I listed (bill structure, tone of grey on dorsum, mirror in P8 etc) would identify an individual as either a red-billed or a silver gull.
Hope that helps
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