Adult birds migrating. My first in Colima. Likely a rather common migrant species, but when they come like this they don't attract much attention, and can easily be overlooked. However, probably mostly because it is not that obvious to bird watch on the coastal side at this locality.
It's a more contrasting bird than Laughing Gull, with brighter upper side and the black wing tips more isolated thus more noticeable.
1 2 cycle, 3cy, bird in the foreground with a likely adult bird in the background. 2 cycle because of the brownish hand coverts, otherwise completely adult plumage.