Animals gathering there (while 'eating').
You would have to distinguish the reason for them gathering (probably by moving closer, thereby scaring them away, then investigating the reason). Not very effective, because they can gather for many other reasons (water, other food, social).
A complication is that these places may be hidden. I remember a salt lick visited by parrots in the Peruvian jungle at the Tampopata river - without prior knowledge you would not see it. It was not an open place like in your picture but an overgrown clay cliff that they clung to:
Credit: Lonni Friedman, FlickrCC
And if you suspect there are around, don't hesitate asking local people ;-)