You are sooo close Colbri… But the long and the short of it is basically a smorgesbord of different senses going on down on the water or over a dump, or where ever they are foraging.
I’ll not offend anyone who posted about Jonathan Livingston Seagull - As Bach is one of my favorites as well.
The reason they are circling, is they are actually foraging. Birds like this find food by scent. The reason vultures circle over carrion is because they are smelling the site, making sure they do not get a scent of disease or some other such sickly rot, that may endanger them. Vultures look like they’ll eat anything, but if they get a sniff of something not Kosher to them, they’ll not eat it. Ever see a vulture or seagul for that matter eat Shit? Oh excuse me… feces? Nope, because there’s a reason…
Seagulls, circle on the thermals because they are smelling for something good to eat… Actually for those who are around seagulls a lot, you may notice something, the ones foraging themselves and eating what the sea has to offer, tend to be healthier than those dumpster diving. It’s because their natural instincts to forage make them smarter healthier than their dumpster counter parts…
Cecil touched on the vulture theme - just do a search and you’ll find it…