In winter, our diving ducks like shellfish and sea worms. Presumably, they swallow shellfish whole, digest them, and poop out the shells. Not sure they can digest a shell.
I wonder whether Buffleheads can dislodge and eat Limpets. My photo is a beach of pure limpets (aka Slipper Shells). Something ate them, and I saw only Buffleheads.
Do we have an expert on diving ducks here?