red-billed gull

Discussion about the evolution, relationships, and naming of New Zealand birds
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red-billed gull

Postby Byrd » Wed Oct 20, 2010 6:47 pm

can anyone tell me why the red-billed gull in the new checklist is now again listed as a subspecies of Australia's silver gull? There didn't appear to be a reason given in the entry. (Unless I missed it; I don't have the book to hand right now)
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Re: red-billed gull

Postby andrewcrossland » Fri Jun 24, 2011 10:51 pm

I can't give an answer to that Q (Infact a lot of the treatments in the new checklist seem at variance with treatments overseas), but one thing I've noticed when flying from NZ to Australia and seeing Red-billed in NZ and Silver Gulls in Australia a few hours later is that (to my eye) eastern seaboard Silver Gulls and NZ Red-bills are pretty much indistinguishable. But Western Australian Silver Gulls are slightly larger, stockier, with a sloped rather than rounded forehead. Has anyone thought that the Tasman Sea may not be the divide between these taxa, but the Australian Bight may well be? AC
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Re: red-billed gull

Postby Byrd » Tue Jul 05, 2011 1:42 pm

since I posted the above in October I have obtained my own copy of the checklist (rather than the library's one), so I just checked it and it says: "Schodde et al (1983), Sibley & Monroe (1990) and Given et al (2005) treated L. scopulinus as a full species but we await the inclusion of L.n. forsteri in a study before adopting this approach"

And coincidentally on Birding-Aus there has been recent discussion over two-mirror vs. three-mirror gulls and so I have lifted the following two posts (the first by David James and the second by Murray Lord) which are relevant to the split/non-split:

Firstly, some comments on taxonomy. Sibley & Monroe (1990) were the first to split them as separate species. Their justification for it was a pers. comm. from Dick Schodde, without any reasons. It has to be said that gulls are not one of Dick’s specialties, and he has not published any taxonomy on the group, either before or in the intervening 2 decades. Splitting doesn’t get much lamer than that, with no science that I am aware of to support a split. Neither Johnstone nor HANZAB found any reason to split them. That some field guide authors follow such splits does nothing to strengthen the lack of arguments in support. The reality is that they are not very different.

Recently I looked at whether anyone had claimed a basis for splitting Australian
and New Zealand Silver Gulls. The only thing I came across was the following. It
is from Given, A.D., Mills, J.A., Baker, A.J., 2005. Molecular evidence for recent
radiation in southern hemisphere masked gulls. The Auk 122, 268–279:

"Recently diverged taxon pairs, such as L. hartlaubii-L. cirrocephalus and L. n.
novaehollandiae-L. n. scopulinus, have evolved distinctive morphological
differences despite occasional hybridization events. The latter pair are isolated
in Australia and New Zealand, respectively, but the two forms differ in size
(especially in tarsus length) and in wing-feather markings. However, because they
otherwise look so similar and in the breeding season have striking red color to
their external soft parts, they are treated merely as subspecies of L.
novaehollandiae. Given that they clearly have independent evolutionary histories
and thus qualify as phylogenetic species, we recommend formally raising each to
full species status as L. novaehollandiae (Silver Gull of Australia and New
Caledonia) and L. scopulinus (Red-billed Gull of New Zealand)."

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