birding-aus

Red-billed vs Silver Gulls

To: "Ross Silcock" <>
Subject: Red-billed vs Silver Gulls
From: "Frank O'Connor" <>
Date: Sat, 26 Jul 2003 19:43:33 +0800
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.

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