At 19:57 1/01/99 +0800, Frank O'Connor wrote:
> a different gull at Lake Monger in Perth. It has very yellow bill, feet
and legs. These were very easy to see by eye
>even from some distance. The upper bill has a faint black tip. Its shape,
>size, etc were all the same as the nearby Silver Gulls, and I believe that
>this is what it is.
It is quite likely that this was just an abberant silver gull. bare parts
colour can vary a bit for many reasons: geographical variation, season,
age, sex, nutriton and just plain simple individual variation, not too
mention chromatic abnormalities. When you look at lots of gulls you will
see that they are particularly variable birds, one reason why they are so
challanging and popular amongst the "larophiles" of the northern
hemisphere. for instance when living in hobart in the late '80s I saw a
couple of adult kelp gulls with blue-grey bills and legs amongst the
thousands I looked at. They were seen in winter (seasonal factor) but were
still odd-ones out (individual factor) and nutrition or health probably
played a role (my guess).
I have photographs of a juvenile silver gull (lots of brown speckles on
wings and scapulars, smudgy head etc) from perth, Dec. 1991. This bird had
pinkish yellow legs and bill with a black smudge at the tip of the bill. My
impression is that bare parts colours are paler and more yellowish or
orangey in the SW rather than balckish red in the east (geographical
component) but I've only just realised that I didn't mention this in the
HANZAB text for silver gull. WHOOPS! It also sounds like you bird may be a
bit extreme (individual component). I'd be interested to know if the
geographical component is real. one complicating factor is that silver gull
was probably much rarer and with a few distinct subspecies 200 years ago.
With the arrival of colonists, fishing boats and garbage dumps they have
become more common, move around more, hybridyze and the subspecies are
disappearing. Young birds with pale bare parts may be the last of a former
the SW subspecies that has been swamped by genetic flow the Bight or
somewher else (just a wlid hypothesis).
>
>Other details of the bird were a white head with a dark (black?) eye with no
>noticable eye ring. The back was silver, but some flight feathers were
>still brown. The flight feathers appeared longer than the nearby adults,
>but almost identical to the other immature gulls. At rest, the flight
>feathers crossed. They were black with three very small white dots visible
>at rest. In flight it had a thin faint dark grey band on the tail tip (or
>very close to the tip).
there aren't many (any?) gulls with identicle shape, size and back
colouration silver gull. Head and breast shape, wing projection, leg
length, bill shape of silver gull is pretty unique.
One remote possibility is Hartlaubs gull, the S. african equivalent of
Silver and frequently treated as same species. however, I think this
species has dark bill and legs like eastern silver gull when young.
The various hooded gulls including common black-headed have rather
different shapes, wing patterns and noticable dark marks on the head in all
plumages.
Common Gull has darker mid-grey upperparts, only has a combination of white
head and yellow bill in adult summer and then has pale eye and different
wing, is a bit bigger, very different.
>
>However, this is the first Silver Gull that I have seen with yellow bill and
>legs, so I looked up HANZAB for more details... suggests that it is a
"first immature". But surely these should be common?
They certainly are common. about 1 in 5 or 1 in ten at the right time of
year in most places. sometimes 1 in 3
If it is a silver gull then I think you are correct in calling it a first
immature. The flight feathers (primaries, secondaries and tail) are
retained from juvenile plumage but he bird has moulted the chquered
juvenile scapulars and some or all of the wing coverts. whether it is first
immature non-breeding or first immature breeding is perhaps trivial.
The major point of HANZAB is to summarise what we know about birds of the
region. By default, if it's not in HANZAB you can consider it NOT KNOWN (it
may be known but not published or it may be lost, what's the difference?).
The obvious step is to publish a short note correcting this. Your
literature search can start and end with HANZAB. May I suggest Australasian
Seabird Group Newsletter as an approriate forum.
Cheers,
David James
PO BOX 5225
Townsville Mail Centre 4810
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