Geese, Ducks, and Questions

Here we have some geese and a turtle. Mr. Turtle often appears in that spot, probably because the geese have worn the shoreline into an area that makes a passable ramp.

So I have a mystery and maybe a reader can solve it. Who is putting tiny shells in my bird baths and why?Here we see a few little shells in the bird bath next to some willow leaves. Someone suggested a crow but I've never seen one on our deck. This happened in two different bird baths. 

I assume the shells are from the lake that is next to our yard. Here are some geese and ducks gathering to be fed on the opposite shore. Someone feeds them every morning around 8:00. Often I hear car horns honking because the geese stand in the road in expectation of being fed. It's futile to honk at them though. I have better luck opening the window and drumming on the side of the door. 

 And finally, some of these guys in flight. I think they're ducks; or do you think they're geese?