Saw two gulls (circled in the picture) among a flock of Black-headed Gulls and Black-tailed Godwits at Pennington Marshes today. While it's not particularly marked in the photo, the two circled gulls had pink flushed underparts and really stood out from the rest of the flock. The photo was taken by a mobile phone through my SLCs and, unfortunately, this pinkness has not been captured by the photo.
Do Black-headed Gulls sometimes have pink flushed underparts or are these birds something more exotic (e.g. Bonaparte's Gull)?
Thanks for any advice or suggestions.