Remsen, J.V. 1978 Black-headed Gull Larus ridibundus Feb.25 Arcata, Humboldt Co., Calif.: 1 ad. at Mad River Slough bridge in the Arcata Bottoms. This bird has been present for a week, but had been identified previously as a Franklin's Gull. Mike and John Parmeter found the bird last weekend and although they had identified it as a Franklin's at the time, they realized that evening that it was not a Franklin's after consulting literature. However several other people subsequently looked at the bird and had concluded it was a Franklin's. When we arrived at the spot, Jon Dunn took one look at the bird sitting on the mud several hundred yards away in miserable, glare-plagued light and instantly called it a Black-headed Gull. Lacking Jon's recent extensive experience with this species in Europe (and Jon's field I.D. skills), I couldn't say it was a Black-headed for sure, but offered to swim across Mad River Slough if the bird was a Franklin's (or any other N. American gull). It was sitting on the mud with 3 Ring-billed Gulls and 3 Mew Gulls. It seemed to be smaller than a Ring-billed but larger than a Mew. The mantle color was virtually identical to that of the Ring-billed Gulls (pale gray), and definitely darker than the Mew Gulls; and so it could not be a Franklin's Gull, which has a very dark gray mantle, and should appear smaller than Mew. While Jon went to find the other carloads of birders in the area, I stayed and studied the bird in much better light and at a closer distance (~200 yds) through the scope as it was swimming on the water. The shape of the bird