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Caspian Gull Larus cachinnans

Caspian Gull photo index
Caspian Gull Photo Index


Scarce but increasing visitor, primarily November to January. At least 214 individuals to 2010.



Discussion

Caspian Gull Larus cachinnans is now widely recognised as a separate species, distinct from both Herring Gull L. argentatus and Yellow-legged Gull L. michahellis. For a detailed taxonomic perspective of these and kindred forms, see:  Yesou, P., 2002, 'Systematics of Larus argentatus - cachinnans - fuscus complex revisited', Dutch Birding 24: 271 - 298. The BOURC has now accepted cachinnans on to category A of the British List and, in 2007, recognised it as a valid species Larus cachinnans.

Taxonomic pre-amble:

While the taxonomy of 'large white-headed gulls Larus' remains a matter of considerable debate, it is increasingly clear from morphological, moult and behavioural studies that the southern complex of yellow-legged gulls (breeding from the region of the Mediterranean basin, east across central Asia and Transbaikalia, to the western fringes of China around Hulun Lake) requires a taxonomic approach distinct from the Herring Gull Larus argentatus. Many authorities now treat michahellis and cachinnans, as well as several other southern forms, as specifically distinct from Herring Gull. Initially, the name Yellow-legged Gull L. cachinnans was applied to this group as a whole, but more rigorous taxonomic and field studies have revealed this approach as unsatisfactory. Within the complex of 'southern' yellow-legged gulls, there are significant variations in morphology and behaviour, and up to seven forms have been recognised, with some considered worthy of recognition at the species level.

Two taxa are currently being identified in Britain. The western Yellow-legged Gull Larus michahellis breeds from the Mediterranean basin east to the southern Black Sea and west to the Atlantic coasts of Iberia, NW Africa, Madeira, the Canaries, and the Azores. It has long been recognised as a regular post-breeding visitor to the southern half of Britain. The population breeding on the Atlantic seaboard and islands is often differentiated as atlantis.

The Caspian Gull L. cachinnans breeds from the Black Sea east across Kazakhstan; populations breeding in the west Caspian Sea area tend to display a different primary pattern from those east of the Caspian Sea and are sometimes distinguished under the sub-specific name ponticus. In recent years, individuals displaying the characters of cachinnans/ponticus have been  identified in Britain with increasing frequency.

Further forms are found in the northern steppes of Central Asia (barabensis); in Armenia, eastern Turkey and NW Iran (armenicus); and from the Altai east though Transbaikalia (mongolicus). Of these forms, it is conceivable that barabensis, which is a long-distance migrant, could reach Britain. The taxonomy of these forms is still controversial. During 2007, and after a long period of deliberation, the BOURC decided to classify barabensis as closely related to heuglini (Heuglin's Gull) and both as subspecies of Lesser Black-backed Gull L. fuscus, while it has grouped mongolicus (Mongolian Gull) and vegae (Vega Gull) with smithsonianus (American Herring Gull). This arrangement is certain to spark vigorous debate and not a little contention.

Finally, it should be noted that - despite the new taxonomic arrangements - the spread north and west of Yellow-legged Gulls and Caspian Gulls has brought their breeding ranges into contact with that of Herring Gull. In Poland, for example, the three forms breed alongside one-another. Assortive breeding supports their classification as separate species but, nevertheless, hybridisation is not rare. Some of the gulls observed in the UK have appeared to show mixed characters, while colour-ringed individuals of known hybrid origin have also occurred. It has also to be borne in mind that, except when colour-ringed birds are encountered, the provenance of the gulls reaching the UK is not known. Consequently, there is a degree of supposition about identification features which have been based upon observations of such extralimital individuals.

More recently (2010 & 2011), based upon individuals of known provenance and genetic origins, Chris Gibbins, Grzegorz Neubauer, Brian Small and John Sweeney published a comprehensive two-part paper in British Birds. Part 2 investigated the issue of natural character variation versus hybrid influence in influencing the appearance of Caspian Gulls. Using a statistical approach, an Index was generated based upon a suite of traits scored from individuals of known 'pure' provenance and of hybrid origin, respectively. This enabled the degree of overlap in appearance to be evaluated and confidence limits to the Index to be calculated, which defined which individuals could be safely assigned as pure Caspian Gulls. As well as confirming a distinctive character to many Caspian Gulls, the results also confirmed that a full suite of features must be observed and evaluated. However, the results also indicated that not all individuals meet the traditional image of a 'classic' individual. For example, 32% of 1W individuals displayed rather coarse markings on the second-generation scapulars (rather than fine anchor marks) while 16% of 1W displayed quite evident streaking on the head and body (rather than a cleanly white appearance).

For anyone interested in these gulls, study of the references at the foot of this note is an essential pre-requisite. The paper by Lars Jonsson provides a clear exposition of the historical debate, and the compelling reasons why several species should be recognised among this complex. These references provide identification details for the range of forms, and include a large gallery of photographs. The papers by Gibbins et al. also discuss and illustrate the problems arising from hybridization. Short of visiting their breeding and wintering areas, study of such photographs is the only way to establish a well-founded appreciation of the structural and plumage characters of the various forms and the problems which need to be addressed.

Garner, M., Quinn, D. & Glover, B. 1997. Identification of Yellow-legged Gulls in Britain. British Birds 90: 25 - 62, 369 - 383.

Gibbins, C., Small, B.J. & Sweeney J. 2010. Identification of Caspian Gull. Part 1. British Birds 103: 142-183.

Gibbins, C., Neubauer, G. & Small, B.J. 2011. Identification of Caspian Gull. Part 2. British Birds 104: 702-742.

Jonsson, L. 1998. Yellow-legged Gulls and yellow-legged Herring Gulls in the Baltic. Alula 4: 74 - 100.

 


Caspian Gull records from the West Midlands Region

Caspian Gulls are now being detected (and photographed) with some regularity at various sites in southern and eastern England. The distribution of records is by no means even, with some sites reporting a much higher incidence than others, in comparison with records of michahellis. Relatively few cachinnans were detected in the West Midlands region before 2003 but the species is now encountered with increasing regularity at landfill sites, gull loafing areas and winter roosts, reflecting no doubt both enhanced observer effort and improved knowledge of the form's characteristics. The first records for the region came from Draycote in 1999 and up to 2010 a total of at least 214 individuals occurred, embracing all four counties. The numbers now encountered mean that published details are increasingly summarised and precise data for individual gulls are more difficult to discern. Also, movement between sites (and even counties) leads to duplication of data. It is likely that 2010 will be the last year for which a reasonably precise determination of numbers can be attempted.

Annual distribution

The annual numbers of Caspian Gulls during 1999 - 2010 (based upon arrival dates) are displayed in Figure 1. Where a series of reports from a particular locality is believed to refer to a single individual, or where a known individual moves between sites, only the date of the first sighting is included in the figures.

Annual distribution of Caspian Gulls, 1999 to 2010

Caspian Gulls have been recorded annually since 1999 (Figure 1). Of the 214 individuals, 113 (53%) were adults or near adults, 19 (9%) were third-winters, 37 (17%) were second-winter and 45 (21%) were first-winter. An upturn in reports began in 2003 and gained momentum from 2006. Numbers reached an apparent peak in 2008 with a decrease thereafter but this is very likely due to more regular observations at key sites detecting 'long-stayers' and individuals moving between sites, thereby reducing the number of 'duplicated' records.

Monthly distribution

The monthly distribution of records during 1999 - 2010 is presented in Figure 2.

Monthly distribution of Caspian Gulls, 1999 to 2010

Caspian Gulls have been reported in all months except May but with a clear peak in the winter months between November and January.

County distribution

All four counties have recorded Caspian Gulls, with 21 (23%) from Staffordshire, 47 (52%) from Warwickshire, 16 (18%)  from Worcestershire and 6 (7%) from the West Midlands County (some individuals were observed in more than one county).

  Total*
Staffordshire 65
Warwickshire 88
Worcestershire 36
West Midlands 45

Table 1. Distribution by county of Caspian Gulls in the West Midlands Region, 1999 - 2007.

* Note that county totals sum to 234 (not 214) as they involve some duplication, with individual gulls being occasionally recorded in more than one county. For example, some individuals roosting at Chasewater, Staffs, have been observed during the day at Stubbers Green, West Midlands.

Key sites are Belvide and Chasewater in Staffordshire; Coton, Dosthill Lake and Draycote Water in Warwickshire; Throckmorton & Westwood Park in Worcestershire; and Bartley and Stubbers Green in West Midlands.


See also:

Dean, A.R. 2011. The status of Caspian Gull in the West Midlands region. West Midland Bird Report (for 2009) 76: 244 - 249.

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