Hello larophiles,
An adult Pacific Gull in Sydney is a remarkable occurrence these days. I don
't have access to most of my files and references at present, but here is
some information I gathered in 1994 when preparing the texts for Pacific
Gull in HANZAB III and the 1995 Wingspan article.
* The complete annual moult of adults is in an advanced state in May.
* 4th yr birds can appear like adults (essentially B&W with fully coloured
bare parts) but with brownish streaks on the nape.
* Pacific never has white apical spots on the outer primaries, but adults do
have apical spots on the inner 5 (or so) primaries. These are not usually
visible when the wing is folded, but they can moult 2 or 3 primaries at a
time, so it may be that the apical spots on the inner primaries are briefly
visible? However, there are other reasons you could see white spots on the
wings (as pointed out already by Dion Hobcroft), so close scrutiny is
needed.
* During the moult, the tail can appear wholly white for a brief period.
This is because the tail moults synchronously (ie 6-12 feathers at a time).
When the new central feathers are growing, their black bands are hidden
under the uppertail coverts, and their white tips cover the black bands on
the outer tail feathers (because, in all birds, iner tail feathers lie on
top of outer ones). So, not only does the tail look white, it still looks
long!. I've never seen this in the field, but have seen it on several
museum skins. It was first reported from the field by Eckert (1971. Emu 71:
61-64), and then again by Robertson (1977; Aust. Bird Watcher 7: 5-10). From
memory, there is a photo in one of these papers.
* The bill of Pacific Gull is diagnostic in several ways: size and shape;
red on both mandibles; round nostril.
* Pacific is a rather aberrant gull, and was long placed in its own genus,
Gabianus. It is not closely related to Kelp Gull (despite appearances, Kelp
is more closely related to Silver than it is to Pacific!), and hybridization
is extremely unlikely.
Hope this info is useful.
Cheers,
David James
Jakarta
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