When I photographed this gull I thought it was the same bird as the similar first-cycle gull of doubtful ID that I was seeing at this spot, which Alvaro Jaramillo has since suggested is a Glaucous hybrid, possibly Glaucous x Herring. But when I examined the picture I noticed the gray mantle, making the bird second- rather than first-cycle, and the dark wingtips, where the other bird was all-white. Two possible IDs with expert support are Thayer's Gull, and Glaucous-winged x Herring.