Mike, thank you for your impressive educational response. I did overlook the color of the right gull's legs.
With your encouragement, I included another photo taken on the same day at the same place below. The right gull has pink legs and is obviously larger (heavily built?) than the gull on the far left, which I think is a Heuglin’s Gull. It appears to me that it has not fully grown into an adult yet as it still has a black tail bar. Its paler mantle makes me rule out the possiblity of being a Slaty-backed Gull or a Heuglin’s Gull. To me, it is a choice between Yellow-legged Gull and Vega Gull. By the size, I lean towards the former, but the extensive head and neck streaking make it does not look right to me. Could you or other experts please comment again?
