A pellet of pieces of shell and pebbles. Found on a pier on the Piankatank, along with some other samples that had been smushed and otherwise disassembled. Diameter of a quarter and quite round. Who do you suppose chucked it up? Grebes, Kingfishers, Loons, Osprey out there: but they’re all fish-eaters.
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This work by Matthew Wills is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.
Backyard and Beyond 
If it was a scavenger (gull?), shell fragments and pebbles might have been attached to the food and been gulped down with the meat/fish. Possible?
Certainly possible! I think…. Owls are famous for their pellets, but a good number of other birds do it as well.