A gull with two mirrors on the Wollongong pelagic, 25/06/2011.
I took four photos (two not so bad, two not so good) of a Chroicocephalus gull towards the end of the Wollongong pelagic on 25th June 2011.
The gull clearly has only two mirrors on P10 and P9 while displaying adult bill and leg colours, so it is unlikely to be from the populations of NSW, Vic, Tas, SA and Qld based on the number of mirrors alone.
The likely culprits are either a Silver Gull from WA or a Red-billed Gull from NZ.
Other points I'd noticed were the slightly shorter, thicker bill. Instead of slightly tapering over its whole length, it only starts to curve over the gonydeal angle, which appears somewhat larger than in the other Silver Gull photos I have.
An excellent paper on the subject of Silver Gull wing patterns, distributions and movements can be found here (Johnstone, 1982).
Any responses are very welcome - please reply to the Birding-Aus thread or drop me an email through the contact page.