Caspian Gull Larus cachinnans
Scarce but increasing visitor, primarily November to January. At least 450 and probably > 500 individuals up to 2015
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.
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 Gulls are now being detected (and photographed) regularly 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 2015 a minimum of 450 individuals had 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, such as feeding and roosting sites (and even movements between counties) leads to duplication of data. In the figures below, the numbers from 2010 onwards are approximations, with some adjustments having been made for birds thought likely to have been seen at more than one site. Countering such duplication, however, is the likelihood that some individuals are not diagnosed as 'new' when occurring at the best-frequented localities.
The annual numbers of Caspian Gulls during 1999 - 2015 are displayed in Figure 1.
Caspian Gulls have been recorded annually since 1999 (Figure 1). An upturn in reports began in 2003 and gained momentum from 2006. Numbers reached an initial peak in 2008 with a decrease over the following three years but increased again from 2012. Of the approximately 450 individuals up to 2014 (full regional age-data is not available from 2015), approximately 50% were adults or near adults, 8% were third-winter, 18% were second-winter and 24% were first-winter.
The monthly distribution of records during 1999 - 2010 is presented in Figure 2 (based upon arrival dates). In subsequent years, tracking and enumerating individuals has become difficult and assessing reliable arrival dates impractical. During the assessment period of 1999 - 2010, 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 first sighting is included in the figures.
Between 1999 and 2010, Caspian Gulls were reported in all months except May, while in late-May 2011 the gap was closed when a first-summer was identified at Bittell Reservoirs in Worcs. However, there is a clear peak in arrivals during the winter months between November and January.
All four counties have recorded Caspian Gulls, with in the order of 160 from Staffordshire, 150 from Warwickshire, and 85 from both Worcestershire and the West Midlands County. Some individuals were observed in more than one county.
Key sites have been Belvide and Chasewater in Staffordshire; Coton, Dosthill Lake iand Draycote Water in Warwickshire; Throckmorton & Westwood Park in Worcestershire; and Bartley and Stubbers Green in West Midlands. However, the species has become rare at the N. Warks sites, with just a single record from Coton in 2014 and none during 2015. This follows the closure of local landfill sites and the same fate seems destined for Throckmorton in Worcs.
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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