I found this on the Guajira Peninsula in Colombia on 13 Feb. At the time I thought it was a Lesser Black-backed Gull, but other have since pointed out the apparently large size, greenish yellow legs (visible in video), and other features, and suggested that it is a Kelp Gull. I could agree, but the bill does not look very heavy to me.
Here are a couple of heat-hazy photos and some almost uselessly tiny video grabs, but I am afraid they are all I have. There is a bigger photo at:
If anyone can make anything of them, please let me know.