The Crowland Gull description by Duncan Poyser
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PBC News The Crowland Gull description by Duncan Poyser |
"The Ring Billed Gull at Crowland was a most interesting bird. Present on the South Bank of the River Welland Half a mile west of Crowland along the Deeping High Bank. Lincs. The bird was located last weekend by John Holmes and was looked for during the week although given very little profile was given to the bird.
"The bird was reported on Saturday 11 March c11.50 by John to Birdnet. I went up to the site ASAP and initially saw only 4 Common Gulls (all bill banded) having turned the car around at Welland Pit a small gathering of Gulls including 5 or 6 Commons had formed on the bank. Without leaving the car I scanned through the gulls with bins and picked nothing out. On grilling with the scope one adult bird immediately drew attention by having a glaring yellow iris. Checking other features rang a few alarm bells. Here is a description.
"SIZE AND STRUCTURE
"The bird was a shade larger than accompanying Common Gulls and stood more upright. The Lower neck was obviously thick set and the bird appeared to have a slimmer profile than Common Gull. In flight the even distribution of weight along the torso did stand out against the more pot bellied Common.
"BAREPARTS
"The bill was only marginally stouter than Common Gull but did appear longer to me. The base colour was a strong yellow and there was a distinct bill band although this appeared brown in certain lights and was not as strong as I would expect on Ring Billed. The legs were quite a bright yellow, although Common Gulls with a similar leg colour were seen. When standing the bird did appear longer legged but this was a general impression not a direct comparison. The Iris was yellow with a black pupil.
"UPPERPARTS
"Head - Domed, Clean White. Nape - Obvious smudgey blotches from the lower nape and onto the sides of the upper neck. Mantle - Grey and concolourous. Tonally very similar to Common, a shade paler in my opinion but certainly not the Argenteus grey of Ring Billed
"REMIGES
"Tertials - The bird showed a broad, contrasty persil white Tertial crescent. Gulls (Grant) has a photo of a bird at a colony with a similar extent of crescenting but less contrast. Secondaries - In flight the bird showed a broad wite trailing edge to the secondaries. Primaries - On the folded wing there were 3 possibly 4 obvious primary spots. In flight the outermost Primary (p10) showed a distinct and large white mirror. Underparts - Clean and White.
"DISCUSSION
"If this bird had not had a yellow iris it would have been a sturdy Common Gull. Having discussed the bird with Paul Flint he says he has seen RBG in Ireland with "several centimetres" worth of white mirror in P10 and the variability in Tertial crescent covered by the photos in Gulls - so these features are within the acceptable variability for RBG. The mantle colour cannot be explained away or the weakness in bill structure compared with classic RBG.
"The yellow iris is diagnostic of Ring Billed Gull and structurally the bird could fit at the weaker end of the spectrum although this could well be a matter of perception and although visibly different from Common how much of this was over analysis? The nature of the neck markings appeared familiar to me as RBG. Would one individual show such extremes of variation for so many features?
"The other options available are much rarer with Yellow irised Common Gull (open can of worms) or the possiblity of a Hybrid Common Gull x Ring Billed Gull (an idea already suggested by Kehoe in Birding World/ August 1992). The bird has left me confused and challenged and speaking to Andy Brown who watched the bird for an hour and a half on 11/3 he is unwilling to put a name to it at the moment.
"I believe the bird to be a subtle and female Ring Billed Gull with a particularly dark mantle for that species. I have seen about 18 RBG Britain in the past 10 years and none were like this bird. Comments and help would be gladly received.
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