Bahrain - wintering ground for Asian species

Bahrain is a state of only 700 sq km in the Arabian Gulf. This country is an excellent place to study white-headed gulls that breed in western Asia (the republics of the former USSR) and eastern Scandinavia. From late August the first gulls arriving on the wintering grounds can be found along the coast. Those birds arriving first are barabensis, and during the wintering months over 85% of the large white-headed gulls belong to this species. The first weeks are spent on the beach but as winter progresses, more gulls move inland and congregate on the Ashkar landfill, roughly halfway down the island. By the end of February and early March 2001, over 4.000 large white-headed gulls were present at the dump, together with 1.000s of Black-headed Gulls, L. ridibundus. At Ashkar landfill, quarries are created by companies exploiting this site to mine for materials used in reclamation areas.

During the last decade, birdwatchers from Bahrain, Britain, Scandinavia, France and the United States all contributed to more knowledge of wintering gulls in Bahrain. Some call them races, others call them species types or taxa. We follow that last classification. It is now generally accepted that the white-headed gulls wintering in Bahrain belong to populations from either the Russian Tundra or the Russian/Kazakh Steppe. From west to east these tax are:

Russian steppe: ponticus – cachinnans – barabensis – mongolicus. Pontic Gull, Steppe Gull, Baraba Gull and Mongolian Gull respectively. The last probably not wintering in Bahrain, but in features close to barabensis and the eastern population of heuglini (taimyrensis / birulai).
From the Russian n tundra: fuscus, Baltic Gull and heuglini, Siberian Gull.

But how do they look like in winter plumage and is it possible to identify certain age classes by diagnostic features in winter plumages? Due to poor information and the lack of extensive ringing programs in most of these taxa (fuscus excluded) this appeared to be very difficult. After our visit we still don't know exactly how to accurately identify spring 2cy birds of the taxon barabensis and this is mirrored by the extensive pages "Mystery Gulls from Bahrain in the barabensis section". However, we do think different types of gulls can be distinguished in the field.

Classification

We prefer to use the classification 2cy, 3cy, sub-adult and adult. We visited Bahrain at the end of February and in early March, and the captions of all the pictures mention the exact date. Note that, in March, a "first winter gull is in its second calendar year (2cy). Since most gulls moult the primaries and secondaries only once a year, these may hold the best clues for ageing. 2cy barabensis still show pointed juvenile (first generation) primaries, second winter gulls show more rounded second generation primaries, etc. Fuscus and maybe other types as well (e.g. some heuglini?) have an irregular moult strategy in the primaries, but such irregularity was not encountered in Bahrain among the barabensis present.

Prior to our trip, literature already revealed barabensis to be the most common species in Bahrain, accounting for over 85% of the birds. The other taxa are much less abundant, with fuscus wintering in low numbers (total during our trip: less than 10). Regarding identification, both fuscus and heuglini stand more or less on their own. Fuscus as the smallest and darkest species, with almost black upper-parts in 3cy to adult plumage. Heuglini in adult plumage is not as jet-black as fuscus, but still up to three shades darker on our 16 step grey-scale than the widespread barabensis. Structurally fuscus is a long-winged bird. By early March, 2cy can readily be identified on jizz and on the second-generation scapulars & often also wing-coverts, which are normally plain blackish grey with a black shaft-streak. Fucus in 3cy is very adult-like and appears jet-black on the upper-parts as well.

This is what is believed to be the migration strategy of the gulls of the steppe: Higher north, two taxa breed in the tundra region of Russia and Scandinavia: fuscus and heuglini. Fuscus is a true long-distance migrant. Radio-tagged birds were followed from the breeding grounds on a non stop flight to the Black Sea. They stayed there for about two weeks, off coast, right in the centre of the Sea. They moved further south to southern Sudan, Kenya and the Victoria Lake district to spend the winter. Its a hazardous journey, but can be explained by lack or unavailability of food resources at more northern latitudes. Imagine these gulls moving south, right into a region where local gulls are dominating over all the food resources. The northern cousins are then forced to move to southern regions, where more food is available. In Bahrain we saw just a few fuscus. They were seen along the east coast, and two singles were seen at the Ashkar landfill. For such a relatively small gull, the dump might not be the best place to compete for food, explaining their absence. Smaller Black-headed Gulls, which were numerous, are well capable to compete with barabensis, being more aggressive and manoeuvre faster. Its believed, only a few tens of fuscus winter in the region.

Heuglini is also not common, but could be found along the coast and in the harbours. Several were present at the dump as well. Maybe some, especially first winters, were overlooked, as first winter plumage and moult strategy is not yet fully understood. As soon as adult-like feathers appear in the upper-parts, identification is easier. Best clues for identification may be a more aggressive, fierce look. As Howard King explained, "a look typical for everything living under the severe conditions of tundra climate." Heuglini comes from far north, and contra barabensis, the time juvenile birds are exposed to the desert climate is relatively short. As a consequence, the white notching on the juvenile wing-coverts and the feather tips in general are in better condition (less worn) in 2cy heuglini. The brown parts are ess bleached as well. However, 2cy heuglini seems to undergo a rapid moult, right after arrival on the wintering grounds. We have seen several 2cy birds which completely renewed scapulars, almost all visible wing-coverts and even the tail. For more information on identification, link to the heuglini section.

Heuglini spread out in winter, from the Bahrain coast southwards, along the coast of Oman, Yemen, Djibouti, Somalia to Kenya. Maybe other (eastern) types are involved as well, but more study is necessary. The taxon taimyrensis (& birulai) and more eastern types as mongolicus and vegae normally take a eastwards route to Japan and the east Asian coasts. However, Howard King has annual records of large heuglini-type birds, which are slightly paler and mainly feed on dead Socotra Cormorant chicks in the colony. Heuglini is probably also a common winter visitor along the south coast of Iran, Pakistan and the states of Gujarat and Maharashtra in India.

We didn't record any mongolicus, which normally winter in eastern Asia, many in Korea and Japan.

One adult resembled taimyrensis, a species from the Taimyr peninsular. In appearance it was a large gull, rather pale grey in the upper-parts and as a far north breeding species, taimyrensis is a late moulting gull. The bird we saw had P1-P4 recently moulted, P5-P10 old, mantle and scapulars worn, median coverts all missing, inner three greater coverts new, rest missing and it was moulting head-feathers. The bill was pale yellow with almost no black markings. Unfortunately, we only saw a single bird.

Over 85% of the white-headed gulls in Bahrain belong to the taxon barabensis, which leave the steppe breeding grounds already in August. They are believed to be true migrants and probably follow the coast of the Caspian Sea, then cross northwest Iran to end in the Tigris valley on their way to the Arabian Gulf. On their trip south, they pass the breeding grounds of nominate cachinnans, which breed along the eastern coastline of the Caspian Sea and probably eastwards. Maybe some of these cachinnans join barabensis on their migration to the Gulf. However, numbers of cachinnans in the Gulf region are very low, although they may be overlooked. Due to great resemblance to barabensis, identification of cachinnans can be hard. Another theory is that cachinnans is not a such a strong migratory species and remain in the Caspian Sea area until it starts to get really cold and they are forced to move southwards. They then disperse to adjacent countries and only arrive in Bahrain by mid-winter.
Being the dominant gull in the area, it's easy to get a general idea of how barabensis looks like. It normally has much black on the outer primaries (commonly on the 8 outer primaries) and the tongue on P10 is often greyish, not white. The head is rounded, accentuated by the rather short, stubby bill, which normally has an obvious gonydeal angle. Of course, larger males show these features more obvious than smaller females. Identification of 3cy birds is rather straightforward as 3cy birds are very adult-like in upper-parts by March. 2cy barabensis proved to show much variation in covert patterns and moult stage by March. We used four classes to group these birds. For more information, see the barabensis section.

The specific identification of taxa within the clinal Steppe Gull-complex remains difficult. In Bahrain, we came across birds resembling the western subspecies of Larus cachinnans, i.e. ponticus, the same we have wintering in NW Europe. In general, they are picked out easy from the widespread barabensis. But what are the exact differences between cachinnans and ponticus? And what is the overlap between eastern cachinnans and barabensis? Most confusion arises from the lack of available literature describing the variation within cachinnans. There seem to be differences on population level in characters such as facial expression; black-white division in the wing; appearance and size of merged tip and mirror; size and shape of black markings on P5 and presence of grey tongues at the outer primaries. On individual level, identification of birds to taxon remains highly speculative. We therefore completely agree with Martin Reid's who notes on his website:

“… note that all identifications of birds in Bahrain are tentative, especially my assignments to race (ponticus or cachinnans) - please interpret each use of a racial name (xxx) as meaning "appears to be closest to xxx based upon population averages".”

Russian studies at the northeast side of the Caspian Sea, showed strong resemblance of nominate cachinnans with ponticus from the Black Sea. This study show much similarity in measurements and upper-part coloration of nominate cachinnans and ponticus. Ponticus is more or less easy to pick out of a group of barabensis and its doubtful that these paler birds are overlooked.

Even in winter, cachinnans does not occur in huge numbers in the Gulf. Probably they take a more westwards migration route to the Mediterranean to spend winter together with their counterparts from the Black Sea, ponticus. Main winter areas of both cachinnans and ponticus are believed to be Israel and Cypress. At least, there are known ring recoveries of these gull-types from this area.

We would like to thank Howard King, Norman van Swelm, Peter de Knijff, Martin Reid & Pim Wolf. Their contributions for the trip and our preparations for this site were indispensable. Nevertheless, it is inevitable that there are some identification/aging errors at this site for which we take full responsibility, and we appreciate any comments and suggestions. Please let us know and mail.

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Bahrain: wintering ground for Asian species