Hard to ID Gulls; Thailand Birding

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On 17th February I took a boat trip onto the sand spit at Laem Pak Bia accompanied by six British birders and Mr Daeng to look for White-faced Plover. On arriving at the sand spit a number of large gulls drew our attention including 5 Pallas’s Gulls and a Black-tailed Gull. Whilst watching these several apparent Heuglin’s Gulls arrived to confuse us. While I am not a gull expert, I am quite adept at spotting something that is different from the crowd and one of the new arrivals was fairly obviously different.

2 adult a at least 3 subadult apparent Heuglin’s Gulls all shared the same structure with a heavy bill and bulky head with heavy brows and large eyes but one bird in the group was noticed by myself, Mr Daeng and several of the group to be of a slightly smaller size and different structure, with a smaller head proportional to the body, a more slender bill, deeper yellow legs with almost orange feet and much smaller, dark, eye. I took a number of photos to attempt to identify the bird properly later on with the aid of Olsen & Larsson’s Gulls of Europe, Asia & North America.

This first photo shows the bird in question. I have cropped it but done nothing else to change the image. The slim bill, small head and small eye can be seen.

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This second photo shows an adult apparent Heuglin’s Gull which was on the sand spit at the same time. The bulkier head, bill and larger eye with heavy brow can be seen.

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This third photo shows the same two birds together, with the Heuglin’s on the left and the mystery bird on the right. Some idea of the size difference can be seen here as can the deep yellow legs of the bird in flight which were obviously deeper yellow than the Heuglin’s when seen side-by-side. Although the angle is tricky this photo also gives some idea of the difference in structure of the head of the two birds.

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This fourth photo shows the mystery bird again. The small headed appearance and small eye are obvious in this photo. Unfortunately, I did not get any photos of the two birds standing together but when we observed them doing so, the mystery bird was obviously slightly smaller.

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Having studied the literature that I have available this mystery bird seems to have many features consistent to “Steppe” Gull Larus (cachinnans) barabensis. Olsen & Larsson write about how this species has a more slender bill and smaller eyed appearance than other similar species as well as often having the darker colouration seen in these photos. They also mention deep yellow legs, deeper coloured than Heuglin’s, with sometimes orangey coloured feet. The smaller size is also consistent as a comparison to Heuglin’s. Furthermore, the colour pattern on the bill of this bird matches that referred to in text and photos in Olsen & Larsson.

While I am certainly not a gull expert, everything about this bird seems to match the features and descriptions of Steppe Gull according to Olsen & Larsson’s book. Furthermore, it would also seem that the Heuglin’s Gull I have photographed matches the photos of heuglini in Olsen & Larsson rather than the tamyrensis that is usually assumed to occur in Thailand.

Comments on these birds would be welcome.

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