Bang Pu: 20 December 2015

Last Sunday, I was invited to join a small talk called “Gull 102” at Bang Pu, Samut Prakan province. The talk was intended to introduce birders into gulls identification. I gave a talk on gulls in Japan where many species overlap with Thailand. After the talk, we went out to test our identification skills immediately in the field. Bang Pu is no doubt, one of the best places to watch gulls in Thailand. Hundreds of Brown-headed Gulls can be seen around Saphan Sookta bridge where visitors regularly feed them. Odd species can occasionally be found in the mix including rarities and several country’s first records.

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The tide was extremely low when we arrived.

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Brown-headed Gull is the commonest species of gulls in Thailand, particularly at Bang Pu.

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First-winter Brown-headed Gull

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While Black-headed Gull is a rather scarce winter migrant. I found several birds mixing in the flock. This one is an adult.

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It didn’t took us long to finally pick out a rarity, a first-winter Slender-billed Gull!

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It shares similar upperwing pattern with Black-headed Gull but with less black markings on the tip in first-winter plumage.

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It was interesting to see that the bird was highly aggressive despite its smaller size.

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Apart from the abundant Brown-headed Gull, we managed to spot several immature and adult Black-headed Gulls and at least 2 first-winter Slender-billed Gulls. The Slender-billed Gull is a rare but regular winter visitor in Thailand and Bang Pu is one of the best places to see it. One of the birds was joining a noisy group of Brown-headed Gulls begging for food just around the start of the bridge.

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Another first-winter Black-headed Gull; note slender bill and more delicate built

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An adult Black-headed Gull being chased by a first-winter Brown-headed Gull; note differences in size and upperwing pattern

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Then someone spotted something interesting! Can you see what’s in the flock?

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It’s a second-year large white-headed gull with very pale appearance. It soon flew in to join the hungry flock close to the bridge.

The evening ended amazingly with a second-year large white-headed gull showing up just before sunset. It was first seen wading through the low tide in the distance then flew in to join the flocks closer to the bridge. Overall, it has very pale appearance making it blend well into the flock of Brown-headed Gulls.

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We concluded that it’s clearly a second-year Mongolian Gull (Larus (cachinnans/vegae) mongolicus)

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It also enjoyed the easy food provided by tourists.

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Upperwing shots show that it has almost completed the post-juvenile moult on the coverts, as well as the very pale and apparent ‘windows’.

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Mongolian Gull is known for its pale and whitish appearance and very apparent ‘windows’. This shot also shows the contrast between the old juvenile feathers and the new second generation of feathers on the coverts.

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It was also quite aggressive and vocal. Its call was surprisingly thin and not as loud as Heuglin’s or Vega Gulls that I’ve heard. The call was also recorded in this video clip.

After watching the large gull up close, we were confident that it was a second-year Mongolian Gull, another rarity in Thailand. Since the taxonomy of these large white-headed gulls is still not fully settled, the Mongolian Gull is sometimes considered as a subspecies of either Caspian Gull (Larus cachinnans) or Vega Gull (Larus vegae) or even a full species of its own, Larus mongolicus. It differs from the more regular Heuglin’s Gull (Larus heuglini) by strikingly paler and more whitish appearance. Even in this second-winter plumage, the difference is very apparent. Apart from the overall plumage, mongolicus also has very striking ‘windows’ on the inner primaries unlike heuglini, and even more apparent than in vegae. The black tail band is also narrower, even though it is hard to tell in this case since its tail feathers are moulting. I was really glad to see this bird since it’s an addition to my life list. We stayed and watched and photographed it until there was not enough light before happily said goodbyes and went on home.

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