Rare visitor. 39 individuals to 2005.

• Discussion
• Records from the West Midlands Region

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, though the full range of (natural) individual variation of the forms remains to be determined. 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 derived from observations of such extralimital individuals.

For anyone interested in these gulls, study of the references at the foot of this note is an essential pre-requisite. Both references provide identification details for the range of forms, and include a large gallery of photographs. Short of visiting their core 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. 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.

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

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 have been detected in the West Midlands region, but there are signs of an increase in the last two or three years, reflecting no doubt both increasing observer effort and improved knowledge of the form's characteristics. The first records for the region came from Draycote in 1999 and up to 2005 (the latest year for which the West Midland Bird Report has been published), a total of 39 individuals occurred, embracing all four counties.

Annual distribution

The annual numbers of Caspian Gulls during 1999 - 2005 (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, only the date of the first sighting is included in the figure.

Figure 1. Annual totals of Caspian Gulls in the West Midlands Region, 1999 - 2005.

Caspian Gulls have been recorded annually since 1999 (Figure 1).  Of the 39 individuals, 25 (64%) were adults or near adults, 6 (15%) were second-winter and 8 (21%) were first-winter. A significant upturn in reports began in 2003. During 2006 and, especially 2007, this increase gathered further momentum, though records from these years have yet to be processed by the regional records committees.

Monthly distribution

The monthly distribution of records during 1999 - 2005 is presented in Figure 2.

Figure 2. Monthly distribution of arrival dates of Caspian Gulls in the West Midlands Region, 1999 - 2005, plotted from summer through winter.

Caspian Gulls have been reported in eight different months but with a clear peak in the winter months between November and January.

County distribution

All four counties have recorded Caspian Gulls, with 19 (49%) from Warwickshire, 11 (28%)  from Worcestershire, 8 (21%) from Staffordshire,  and just two from the West Midlands County (one of which had been observed earlier in Warks).

Table 1. Distribution by county of Caspian Gulls in the West Midlands Region, 1999 - 2005.

* Note that the same 1W bird was recorded at both Coton (Warks) and Frankley (W Mids) in 2005.

Key sites are Draycote Water in Warwickshire, Belvide in Staffordshire, and Throckmorton & Westwood Park in Worcestershire.