The following are some photographs of an unusual Silver Gull seen at Lake Monger in Perth in January 1999. This is is the first Silver Gull that I have seen with yellow bill and yellow legs.
Dave Mitchell first saw the bird in the south west corner of the lake near the willow trees close to the shore near the island. I visited Lake Monger on the afternoon of Friday 1st January 1999 and very quickly found it. The yellow bill, legs and feet stood out quite clearly. Apart from these, the bird otherwise looked very much like an immature Silver Gull at rest.
It had very yellow bill, feet and legs. These were very easy to see by eye even from some distance. The upper bill had 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.
Other details of the bird were a white head with a dark (black?) eye with no noticeable 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).
I visited Lake Monger again on Sunday 3rd January. I tried a few times to make it fly. It did so but never in company with other gulls to compare. However, it looked to be the same wing span as a Silver Gull. Certainly not dramatically larger. The yellow was more of a very pale orange when I checked.
It fed in the shallow water by stamping its feet to stir the mud, just as many other Silver Gulls were doing, and as recently described in a discussion thread on the birding-aus mailing list.
It normally spent its time slightly separated from all the other gulls, but then all of a sudden it adopted a stretched out position with neck down and head up and followed an adult Silver Gull along the shore and it was 'mewing'? like a juvenile. The adult called raucously back and did not feed it even though the immature put its bill very close to the bill of the adult. The yellow billed immature kept following for a while before resuming feeding.
However, this is the first Silver Gull that I have seen with yellow bill and legs, so I looked up the Handbook of Australian New Zealand and Antarctic Birds for more details. You need to spend some time looking for information in HANZAB, but what I found fairly quickly suggests that it is a "first immature". But surely these should be common? David James who wrote the entries for the gulls in HANZAB sent me the following information :
"I have photographs of a juvenile Silver Gull (lots of brown speckles on wings and scapulars, smudgy head, etc) from Perth, December 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 orange in the SW rather than blackish 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 your 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, hybridise and the subspecies are disappearing. Young birds with pale bare parts may be the last of a former south west subspecies that has been swamped by genetic flow from the Great Australian Bight or somewhere else (just a wild hypothesis). "
"They certainly are common. About 1 in 5 or 1 in 10 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 the bird has moulted the chequered juvenile scapulars and some or all of the wing coverts. Whether it is first immature non-breeding or first immature breeding is perhaps trivial. "
As for being common (1 in 5), I have spent a lot of time scanning flocks of gulls for something different, as Franklin's Gull seems to always turn up each year somewhere in the south west. The yellow on this bird stood out very clearly, and I am sure that I would have noticed it if I had seen it in the last two or three years. There are a few gulls that have yellow mixed with black on their bill, but their legs are either reddish or dark.
This bird was a Silver Gull, but as several people suggested to me, it could have been a Common Gull (Larus canus). Looking at Seabirds of the World (Harrison) and Birds of The World, it certainly looks just as likely to have been a Common Gull.
David James comments that "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."
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