Red-billed vs Silver Gulls

["Frank O'Connor" <>]

At 14:40 24/07/2003 -0500, Ross Silcock wrote:
> Interesting discussion by Rohan on diffs
> between Silver and Red-billed
> Gulls.  The following pics show the difference in P8 (alt plumage)
> very
> well- shouldn't be too tough to pick out in flight.
> Ross
>
> http://www.justbirds.it/Australia/Silver%20gull.jpg
>
> http://www.stanford.edu/~petelat1/00020448.jpg

Have I read this correctly that you are suggesting that you can identify
the two based on whether there is a window in P8?

I don't think that this is true?  Ron Johnstone at the WA Museum
published a paper on Silver Gulls in Australia :

Johnstone, R.E., Distribution, Status and Variation of the Silver Gull
Larus novaehollandiae Stephens, with Notes on the Larus
cirrocephalus species-group, Records of the Western Australian Museum
1982, 10(2):133-165

He says that he can identify Silver Gulls to which part of Australia that
they bred based on the size and number of primary windows, and a few
other characteristics such as the tips of the primaries.

In particular, the Silver Gull north of Shark Bay in WA doesn't have a
window in P8.  Similarly in the Recherche Archipeligo on the south
coast of WA.  In between the window is very small.  In New
Caledonia, only P10 has a window.

Ron sent me this paper, when I was asking about a gull I saw in Broome in
February 2002 with no windows in the primaries and a longer slender
bill.  I wanted it to be a Slender-billed Gull, but I had to
conclude that it was a Silver Gull, maybe from the New Caledonia
population.

_________________________________________________________________

Frank O'Connor           Birding WA http://birdingwa.iinet.net.au

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