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THE 'AMERICAN HERRING GULL' AT CHEW
by Andy Davis and Keith Vinicombe

On Thursday 8 May, I (AHD) noticed an unusual gull in Heron's Green Bay, feeding on a large dead pike on the dam wall. Its behaviour, coupled with its large size and dominant, long, powerful looking bill suggested Yellow-legged Gull. However, before it flew off towards Moreton Point, I noticed that it showed pink legs, which left me puzzled. I didn't see it again that day but on Sunday 11 May I saw it from Herriott's Bridge feeding on a large fish off the Main Reeds. It was very aggressive towards a smaller Lesser Black-backed Gull. The long powerful bill caught the attention again but the colour of the upperparts clearly pointed to a Herring Gull rather than a Yellow-legged Gull. At lunch time the following day, I watched it in flight for five minutes from Stratford Hide as it circled over the lake. I tried hard to concentrate on the primary pattern, but further searching that day was curtailed by my discovery of the Great Reed Warbler at Herriott's Bridge!

I mentioned to Keith Vinicombe and Richard Mielcarek the possibility of the bird being an American Herring Gull (which has recently been split by the BOU). While I was away in Poland the following week, RM saw the gull on Herriott's Pool on a couple of occasions and, on 23rd, he was able to take a photo of it (right). He was able to confirm that it had pink legs and that the size, structure and bill looked very good for a "Smithy".

 


23 May (Richard Mielcarek) This slightly blurred shot shows why the bird consistently stood out: note its large size, its distinctive head and bill shape and its deep breast in comparison with two Lesser Black-backs (a worn first-summer and an adult). Its aggressive behaviour and its Yellow-legged Gull-like fish scavenging were also distinctive.      

I saw it again on 27 and 29 May and I was able to watch it at close range for about three hours on the overspill at Herriott's Pool. At last I was able to study it in more detail. It obviously disappears on its own around the lake or further afield but it seems to come back to the pool in the early/mid-afternoon to wash and preen, after which it again vanishes. These long close-range views revealed the following:

STRUCTURE It was a large, sturdy short-legged gull with a long powerful thick-looking rather parallel bill that recalled Yellow-legged Gull. It had a noticeably hooked tip to upper mandible. It appeared deep-chested with a relatively small head, which often showed a sloping forehead and a flat crown. This, together with the long, heavy bill, gave it a really mean look. When walking on the spillway, it could look very awkward indeed: this was due to its short legs but the deep chest also gave it a front-heavy appearance. In fact I thought it looked very 'duck-like' when it was walking, with a breast-down/back-end-up posture (see photo below). The central tertials were longer than the others, producing quite a pointed shape. In flight it was quite broad-winged with fairly slow beats.

BARE PARTS The eyes were very pale, appearing whitish-olive. The orbital ring seemed pale pink in the field (but some digital images show a yellowish shade [it was definitely yellow on 31 May - KEV]). The legs were short and thick-looking (note that the tarsus was short). They were pale pink [although later observations revealed a slight but distinct yellow tinge to the top of the legs - KEV]. The bill was bright yellow with a bright red gonydeal spot. It also showed a small black mark on the upper mandible immediately above the red spot but this diminished in prominence during the bird's stay.


18 May (Andy Davis) Note the long thick bill, the small black mark above the red spot, the very pale eye and the pale upperparts. Note too its very distinctive shape: the small head with a low forehead, a flat crown and a vertical nape, the deep 'duck-like' breast and the short thick legs


27 May (Gary Thoburn) Again note the long thick bill with a prominent hooked tip, a faint dark mark above the red spot and the smooth head shape with a low sloping forehead


VOICE I heard it calling on 29 May: it was deeper than the calling Lesser Black-backs close by.

BEHAVIOUR It could be very aggressive when feeding on a fish but, on 29 May, it hung back from the all the Lesser Black-backs fighting for bread and just called for a few minutes.

Andy Davis
3 June 2008



Following Andy's intriguing observations and his suggestion that the bird was an American Herring Gull, I tried on several occasions to see it but without success. On 30 May Richard Mielcarek was able to take a close-up photograph of P5 and this clearly revealed a sharply pointed 'W' shape, a perfect pattern for American Herring Gull. I caught up with it at long last on Saturday 31 May when I was able to take 85 photos, mainly as it preened at only 15 yards range on the metal valve adjacent to the spillway on Herriott's Pool. I was able to obtain good photos of P5, P6, P7, P8 and P10 as well as mediocre shots of the open wings from above and below. Adult American Herring Gull has a different primary pattern from both argenteus and argentatus European Herring Gulls and later that evening I was able to compare my photos with the detailed paper by Peter Adriaens and Bruce Mactavish in Dutch Birding (2004) 26:151-179. Adriaens and Mactavish stress that there is no individual feature that is diagnostic of adult American Herring Gull but they list a series of percentages that indicate the likelihood of the three forms (smithsonianus, agenteus and argentatus) showing any given primary pattern. My photos clearly indicated that the bird was closest to smithsonianus.

Another point worth mentioning is that the bird was extremely aggressive, often making unprovoked and quite violent attacks on Lesser Black-backed Gulls that were sitting on the water and minding their own business. I have never seen other gulls do this. I also heard it call at close range and I can confirm that the call is very distinctive, being very deep - deeper than Lesser Black-back, and gruffer.

On 1 June, I discovered that Gary Thoburn had also taken some shots of the bird on 27 May and he kindly forwarded them to me. As is usual with Gary's photos, they were first class. Fortunately, he had taken a cracking flight shot that clearly showed the precise pattern of the upper primaries as well as P10, P9, P8 and P7 on the underwing (see below). I was able to check this against photographs in Adriaens and Mactavish, Gulls of North America, Europe and Asia by Klaus Malling Olsen and Hans Larsson, The Large Gulls of North America video (The Advanced Birding Series - Peregrine Video Production) narrated by Jon Dunn, photos of the Galway bird in the Galleries section of www.birdwatch.co.uk, and with some excellent shots that Bruce Mactavish had sent me earlier in the year. One of Bruce's shots - photographed in Newfoundland in February - showed a primary pattern that was, to all intents and purposes, identical to our bird. I forwarded this to Andy and we agreed that, in combination with the structure, bare part colour, upperpart colour and call, it confirmed beyond any reasonable doubt that the bird was an American Herring Gull.


LEFT: 27 May (Gary Thoburn) This flight shot shows the pattern of the primaries. On the far right wing, note the long pale wedge on the inner web of P9 and the long pale wedges on the inner webs of P8 and P7, which are similar in length. On the near left wing, note that the white mirror on P10 is separated from the small white tip by a complete narrow black band; on P9 the small white mirror is confined to the inner web; note the long grey wedge on the inner web of P8 and the distinctive pointed shape of the black marks on P7 and P6, with a sharp point of black (or 'bayonet') extending up the outer edge of each feather. Note also the sharply pointed 'W' mark on P5 and the white tips to the grey inner 'tongues' (or wedges) on the inner webs of P7, P6 and P5. All these features are typical of American Herring Gull.

RIGHT: Newfoundland, February 2008 (Bruce Mactavish) Compare the two photographs: the pattern of the primaries is, to all intents and purposes, identical.



This represents the second Chew record, following the fourth-winter that was seen intermittently from 29 December 2007 to 8 February 2008. A previous record of a first-winter seen from Wick Green Point on 13 March 2004 was not submitted owing to less than perfect views.

The really boring bit...the primary pattern (all photographs below taken on 31 May by Keith Vinicombe)


P5 This showed a sharply pointed 'W' mark with a white subterminal 'tongue tip' to the grey inner primary wedge.


P6 and P7 (above) Both feathers showed a sharp black 'bayonet' shaped extension up the edge of the outer web (and up the shaft on P6). There was a white 'tongue tip' on the grey wedge of P6; although in this photograph such a mark does not appear to be present on P7, it can be seen in Gary Thoburn's flight shot. Again, all these features are characteristic of American Herring Gull.

 


P8 This feather had a long pale wedge on the inner web which appeared to be similar in length to that on P7 (also confirmed in Gary Thoburn's flight shot).

P9 (see Gary Thoburn's photo on 27th May) The grey wedge was longer than half the exposed feather length (this is true of more than 98% of Newfoundland smithsonianus but only 59% of argenteus). Another pro-American feature was that the white mirror is confined to the inner web.


P10 Newfoundland American Herring Gulls show a long pale grey wedge on the inner web, rather like Caspian Gull. In this respect, our bird did not conform to Adriaen's and Mactavish's findings in that the pale on the inner web was confined to an elongated triangle at the base of the feather. This pattern was not totally wrong for Newfoundland American Herring Gull, but only 7.8% showed it, compared with 95.6% of argenteus. However, the December-February Chew bird showed an identical pattern, as did the 2007-08 Galway adult (www.birdwatch.co.uk). Further investigation indicated that American Herring Gulls from the Canadian interior, as well as many from the Great Lakes and a higher proportion wintering in Massachusetts, show an identical pattern (an example of such a bird can be found freeze-framed on The Large Gulls of North America video, filmed in northern Ohio). Also, Olsen and Larsson (page 245) in fact give an all-black P10 as standard for American Herring Gull. As with European Herring Gulls, there is considerable geographical variation in American Herring Gulls, with northern birds showing more white in the primaries than southern, interior and West Coast birds. It seems likely, therefore, that our vagrants may be originating from inland Canadian colonies, rather than from the closest source, which is Newfoundland. This may actually make sense, as the birds from the inland populations are clearly more migratory, heading south-east to winter on the Eastern Seaboard. The complete narrow black line between the mirror and the small white tip is also characteristic of American Herring Gull.

Summary

PRIMARIES To give an indication of the relevance of the individual primary patterns shown by our bird, the following indicates the percentage of each form that have the individual feather patterns shown by our bird. This is based on the Adriaens and Mactavish paper in Dutch Birding; note that the patterns on P9 and P8 of the Chew bird are slightly intermediate to the precise patterns illustrated by them:

  Newfoundland
smithsonianus
argenteus argentatus
P10* 7.8 95.6 53.1
P9 23.5 8.4 45.7
P8 55.4 0.0 10.8
P7 38.4 1.1 5.6
P6 95.0 62.3 55.6
P5 70.2 3.4 0.0
Totals 290.3 170.8 170.8

* If you ignore P10 for the geographical reasons outlined in the caption above, the figures become even more convincing:

Totals 282.5 75.2 117.7



Another showing the underneath (Jeff Hazell).



As well as showing the obvious size and structural differences from the argenteus on the railing, note also the longer primaries and the different primaries and tail ratio, with more white primary tips visible. Recordings of its long call sound similar to those of American Herring Gull: a deep, rather husky staccato bellowing that slows up towards the end (KEV).



Other features

Of course you have to evaluate the primary pattern in conjunction with the other pro-American Herring Gull features revealed in the photographs:

SIZE Very large size, intermediate between European Herring and Great Black-back (but closer to the former).

BILL Noticeably long and heavy with a strongly hooked tip.

BILL COLOUR Small black mark on upper mandible persisting into late May.

HEAD SHAPE Smallish looking head with smooth profile and low and rather flat forehead.

BREAST Deep-breasted impression creating 'duck-like' shape.

LEG LENGTH Short and thick.

LEG COLOUR Pale pink (but with a yellow tint at the top of the legs which is compatible with some American Herring Gulls in breeding condition).

EYE COLOUR Very pale eyes.

UPPERPART COLOUR Pale grey upperparts, similar to argenteus (correct for American Herring Gull but of course incorrect for argentatus).

PRIMARY COVERTS A high proportion of adult or near adult American Herring Gulls show dark markings on the primary coverts, varying from black lozenge-shaped marks to fine black shaft streaks. Our bird showed the latter. (see Lonergan and Mullarney (2004) [Dutch Birding 26: 1-35]).

BEHAVIOUR Although not mentioned by Adriaens and Mactavish, the aggressive behaviour of our bird towards the other large gulls is noteworthy, as is its habit of feeding on dead fish. This is something that European Herrings do not habitually do at Chew, although it is the preferred feeding method at the lake by both Yellow-legged and Great Black-backed Gulls.

VOICE Distinctly deeper calls than argenteus (subsequently confirmed from tapes of American Herring Gull).

Keith Vinicombe
4 June 2008


Acknowledgements: Thanks to Rich Andrews, Paul Bowerman, Richard Mielcarek and Gary Thoburn for their help.

POSTSCRIPT - January 2009 [Rich]

Whilst the bird was being watched, it was seen to drop a feather as it preened at the overspill. The feather was collected, and was sent to Prof. Gareth Jones at the University of Bristol for DNA sampling. He was able to obtain a good sequence from the feather, and you can see his results here.


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