AN INTRODUCTION TO THE IDENTIFICATION OF AN ADULT WINTER MEW GULL ON THE AZORES, THE FIRST FOR THE WESTERN PALEARCTIC
By Peter Alfrey
This summary paper is a concise version of a more detailed article, which is due for future publication. Any comments would be most welcomed and/or for a preview of a more detailed article please email me with a request in the subject box on firstname.lastname@example.org.
On 18th February 2003 I was watching a pre-gull roost on the beach of Praia da Vitoria, Terceira, Azores when I came across a very unusual ‘Common Gull’ Larus canus ssp. The bird had a distinctive long necked and small-headed structure, showed a pale olive-yellow iris and when in flight, extensive white in the wing tip was striking. With other birds in the vicinity including thirty three Ring Billed Gulls, a 1st winter Bonaparte’s Gull, four American Herring Gulls and a 1st winter Forster Tern my thoughts turned to the American form of Common Gull, L.c.brachyrhynchus or Mew Gull. Upon returning to the UK, various identification consultants were approached, and after much discussion the bird was concluded to be a Mew Gull - a first for the Western Palearctic.
Mashuq Ahmad visited Terceria in March 2003 and on relocating the bird obtained a detailed photographic record, which contributed towards securing the identification.
In the majority of postures it was slimmer bodied and more elongated than either a second-winter Common Gull L.canus canus(also present) and Ring Billed Gull. In comparison to the Common Gull it appeared relatively long necked with a small rounded head and a slim bill.
The iris was olive-yellow which contrasted strongly with the pupil. This striking feature was immediately obvious. The bill was slender with poorly demarcated sub-terminal markings.
Fig 1. click to enlarge Mew Gull L.c.brachyrhynchus, Terceria, Azores, February 2003 (Peter Alfrey). The long neck, small rounded head, slim, poorly-demarcated bill and pale eye create an immediate distinctive impression. Additionally note the diffuse ‘smudging’ to the nape and breast sides with the light flecking over the head and crown. All these features are typical of Mew Gull L.c.brachyrhynchus
Fig 2. click to enlarge Mew Gull L.c.brachyrhynchus, Terceria, Azores, February 2003 (Peter Alfrey). The structural and bare part features create a very distinctive bird, quite unlike Common Gull.
The head markings were diffuse with a dark grey-brown wash on the hind neck extending faintly on to the breast sides. There were diffuse, ill-defined flecks on the crown and head.
The upperparts were uniform grey-blue obviously darker than the accompanying Ring-billed Gulls and considered slightly darker than the nearby second-winter Common Gull.
The general impression of the primary pattern in flight was one of more pale and less black than typical Common Gull. Large white tongue-tips on P8 to P5 linked with mirrors on P10 and P9 to produce a ‘string of pearls’ effect running along the wing tip. P9 showed a grey pale base extending to over 40% of the inner web (from primary coverts to primary tip) and P8 displayed an extensive pale tongue tip and pale base. Importantly the pale tongue tip to P8 extended to the basal edge of the P9 mirror. A dark mark on P4 was evident. Additionally the white trailing edge to the secondaries and inner primaries was broad, contrasting strongly with the grey upperparts.
Fig 3. click to enlarge Mew Gull L.c.brachyrhynchus, Terceria, Azores, February 2003 (Peter Alfrey). The main features here are the ‘string of pearls’ formed by the pale tongue tips of P8 to P5 connecting with the white mirrors on P10 and P9. Importantly the large pale tongue tip on P8 reaches the basal edge of the mirror on P9 and there is a dark mark on P4. Also important features are the extensive pale bases to P9 and P8 and the complete band on P5.
The identification of Mew Gull has been discussed by various authors, e.g. Dwight (1925),Grant (1986), Tove (1993) and Carey & Kennerley (1996). More recent detailed commentary of the complex has been provided by Raty (2001), Doherty & Oddie (2001), Dunn & Van der Poel (1999) and Olsen & Larsson (2004). Additionally Mashuq Ahmad and myself have conducted extensive museum and field research.
The ‘Common Gull’ complex
There are four forms in the Common Gull complex: L.c.canus (Common Gull), L.c.heinei (Russian Common Gull), L.c.kamtschatschensis (Kamchatka Gull) and L.c.brachyrhynchus (Mew Gull). The old world ‘Common Gulls’ show clinal variation from west to east with the palest and smallest birds (Common Gull) to the darkest and largest birds (Kamchatka Gull). Mew Gull is isolated in this respect and is the Nearctic counterpart to Common Gull from which is differs in structural, plumages and mitochondrial DNA (Zink et al 1995). These factors have contributed towards Malling Olsen and Larsson (2004) assigning this form to full species rank.
Although there is no single fully diagnostic feature to distinguish Mew Gull from the other forms in the ‘common gull complex’ there were many features, which in combination are diagnostic of Mew Gull. These features shown on the Azores bird were:
WING TIP PATTERN
- String of pearls formed by white tongue tips to P8-P5 merging with the P10 and P9 mirrors. (Figs 3, 4, and 5)
In other members of the Common Gull complex this feature is generally absent.
- Pale grey or greyish white tongue on P8 extending to greater than 50% of inner web with broad white tongue tip which extends equal to or beyond the basal tip of the P9 mirror and beyond the tongue tip of p7. (Figs 3, 4 and 5)
In Common Gull and Russian Common Gull a broad white tongue tip is very unusual and when present does not extends to the basal edge of the mirrors on P9 and P10 (pers comm. Mashuq Ahmad). Kamchatka Gull is more variable but can be eliminated from Mew Gull on structural and other plumage features.
- Pale grey tongue on inner web of P9 extending to 40% of inner web from the tip of the greater primary coverts. (Figs 3, 4 and 5)
This amount of grey on P9 is unusual on all forms of Common Gull and this feature is a supporting characteristic in combination with other features.
- Complete sub-terminal band across both webs of P5 (Figs 3, 4 and 5)
This feature is regularly present on all Common Gull forms but when present in conjunction with a ‘string of pearls’ and a broad white tongue tip which lines up with the basal portion of P9 is highly significant and indicative of Mew Gull.
- Dark mark on inner web of p4 (Figs 3, 4 and 5)
This feature is regularly present on all Common Gull forms but when present in conjunction with a ‘string of pearls, complete band on P5 and a broad white tongue tip (which lines up with the basal portion of P9), is highly indicative of Mew Gull. When combined with structural and other plumage features a diagnosis is possible.
- Broad white trailing edge to secondaries and inner primaries
Tends to narrow towards the inner primaries on the other forms of Common Gull.
Fig 4. click to enlarge Mew Gull L.c.brachyrhynchus, Richmond, British Colombia, Janaury 2005 (Mike Danzenbaker http://www.avesphoto.com). Note the ‘string of pearls’ running along the wing tip and the black band on P5. The tongue tips are broad and extensive and note how the tongue tip of P8 aligns with the base of the P9 and P10 mirrors. Additionally, many Mew Gulls show a mark on P4 and a complete ‘unbroken band’ on P5.
Fig 5. click to enlarge Common Gulls L.c.canus, April 29th, 2005, Helsinki Lauttasaar, Finland (Matti Rekila, Tarsiger.com). Note the extensive black in the wing tip compared to Mew Gull - in particular, the extent of black on p8, lack of ‘string of pearls’ and amount of grey on the inner webs of outer primaries.
- Long neck, small rounded head, high breasted
Mew Gull is the smallest of the Common Gull quartet. For structural features for Common versus Mew Gull see Fig 7 and Fig 8. Kamchatka Gull is the largest of the ‘Common Gulls’ and has brutish, heavy billed demeanour quite unlike Mew Gull and in fact reminiscent of Ring-billed Gull.
Fig 6. click to enlarge
Adult winter Mew Gull L.c.brachyrhynchus
, Monterey, California, November 2005, (Bob Steele, http://www.bobsteelephoto.com
/). Note the small head, steep forehead and narrow fine bill. Also the fine bill has indistinct sub-terminal bill markings. The dark smudging on the nape and breast sides grades into the fine flecking over the crown and head. The eye is pale and contrasts strongly against the pupil.
Fig 7. click to enlarge Adult winter Common Gull, L.c.canus, UK (Richard Ford, Digital Wildlife). Note the z-shaped sub terminal markings on the heavier bill, the dark streaking over the head and nape and the dark eye. Also note that compared to Mew Gull, Common Gulls have a ‘larger’ less rounded head and are shorter necked.
- Relatively pale grey upperparts
Compared to Kamchatka Gull, Mew Gull is obviously paler.
- Yellow-olive iris, contrasting strongly with the dark pupil
Common and Russian Common Gull very seldom show a pale eye. This feature is more regular on Kamchatka Gull and is indicative of Mew Gull.
- Dirty grey-brown wash over nape and breast sides
Raty (2001) described this feature as ‘virtually diagnostic’ of Mew Gull.
- Indistinct sub-terminal bill band
A z-shaped bill band is typical in the winter plumage of Common and Russian Common Gull. Kamchatka Gull is more variable.
- Slender bill with a tapering tip to the upper mandible
A typical Mew Gull shows a relatively small bill. In comparison Mew Gull also shows the finest bill structure in the Common Gull complex.
There have been previous claim in the Western Palearctic of ‘common gulls’ showing the characters of Mew Gull. However, the features that separate the various forms have become clearer over the past few years, and subsequently have shown that these prior claims fit within the normal variation of Common Gull. Taken holistically, the gull discovered at Terceria displays all of the features associated with Mew Gull and if accepted it will be the first record of this taxon in the Western Palearctic.
Thanks to Peter Adriaens for instruction and comment and for critically examining the original photographs, providing insight which led to the confirmation of the identification and for providing essential references. Thanks to Mashuq Ahmad for thoughts and contribution. Thanks to Laurent Raty for comments and confirmation and Richard Millington for providing confirmation and comments from various Birding World identification consultants. Thanks to Darryl Spittle for improvements in the text. Thanks to the Natural History Museum at Tring for access to specimens and resources. Thanks to Steve Howell for comments. Many thanks to Martin Reid for identification comments and for providing references and contacts. Paul Lehman helped out with information on vagrancy distribution of Mew Gull and Kalev Rattiste for supplying extensive photographs of wing tip patterns of canus from Estonia and discussion. Thanks to Martin Elliott for discussion and provision of useful video footage of Mew Gull (pers comms M.Ahmad). Also thanks to Brian J Small, Michael Shepard and Alvaro Jaramillo for comments and photographs. Thanks again to Mike Danzenbaker (http://www.avesphoto.com), Matti Rekila, (Tarsiger.com), Bob Steele (http://www.bobsteelephoto.com) and Richard Ford (Digital Wildlife).
References/ Further Reading
Mew Gull Photos in Surfbirds Galleries
| Common Gull Photos in Surfbirds Galleries
Allaine D. and J.D Lebreton 1990 The influence of age and sex on wing tip pattern in adult Black Headed Gull Larus ridibundus. Ibis 132:560-567
Carey G.J & P.R Kennerley 1996 “Mew Gull”: the first record for Hong Kong and the identification and systematics of Common Gull forms in East Asia. Hong Kong Bird Report. 1995 134-149
Cramp, S & Simmons K E L 1983 The birds of the Western Palearctic 3. Oxford
Doherty P & W.E Oddie 2001 Gulls: a video guide to the gulls of Europe, Asia and North America. Bird Images Videos. Yorkshire.
Dunn and Van der Poel 1999 Advanced Birding Video Series. Video 2. The Small Gulls of North America.
Dwight J 1925 The gulls Laridae of the world; their plumages, moults, relationships and distribution. Bull. Amer. Mus. Nat. Hist. 52:63-401
Grant P.J 1986 Gulls: a guide to identification. Second Edition. Calton
Groot Koerkamp. G. 1987 Common Gull with a pale iris. Brit. Birds. 80 :628-629
Kwater, E. 1992 Pennsylvania’s first Mew Gull, with notes on its racial identification. Pennsylvania birds 6:8-9
Malling Olsen K & Larsson H 2004 Gulls of Europe, Asia and North America .Helm
Raty L 2001 ID Frontiers From the internet: http://listserv.arizona.edu
Shepherd, K.B & S.C.Votier 1993 Common Gull showing characters apparently consistent with North American race. Brit. Birds. 86:220-223
Shitega Y. 1993 Common Gull-an attempt to examine the subspecies of Common Gull occurring in Japan. Birder 7:36-41
Sibley D 2000 The North American Bird Guide Mountfield
Strangemann, P.J 1982 Bill colour of winter adult Common Gull Brit. Birds. 75:289-290
Stejneger, L (1885) Results of Ornithological Exploration in the Commander and in Kamtschatka. Bull. U.S Natn. Mus.29.
Svensson L.,P.J.Grant, K Mullarney & D. Zetterstrom 1999 Collins Bird Guide, London.
Tove, M.H 1993 Field seperation of Ring Billed, Mew, Common and Kamtchatka Gulls. Birding 25:387-401
Vaughan, H. 1991 Common Gulls with pale irides. Brit Birds 84:342