This other species is also found at Bang Poo and according to the books, you can tell it apart from the Brown-headed Gull, because of its dark eye, so different to the clear green one in the Brown-headed...

However, as you will see in next image, the juveniles of Brown-headed Gull, also show dark eyes some times, been the markings on the wings, the only way to tell them apart...

I chased this one for a while to get the image when it finally landed on the water...