Chickens turn their beaks up at store bought eggs

Observation :
Our hens completely reject store bought egg shells.
Normally, when we toss kitchen scraps to our hens, the first thing they get after are the egg shells. They fight over them. This last month,  we had an egg shortage, so settled for a couple flats of store bought white eggs.
The hens refuse to eat the white shells. Now I have white egg sells littering their grazing area.
I never would have guessed that hens would be so discerning.  It is kinda funny, but also creepy, what do the hens know that I don't.  
Maybe the eggs have a residue on the shells, maybe they have little minerals in them???
It is not the color, as some of our fresh eggs are white.
Has any one had a similar experience?  

That's a fantastic observation! I'm also a little creeped, as you mentioned, what do they know that we don't? I'm intrigued! Thanks for sharing!

It's hard to say why a chicken rejects something or not. I'll occasionally throw egg shells to mine--there are long stretches where they devour them and long stretches where they reject them. Who knows why?

That is interesting.  Might they turn their beaks up at them because they don't need calcium because they aren't laying?  Could you hold on to some of them until spring and see if they eat them then?

After reading the original post, it reminded me of occurrences I read in a book several years ago about observations of wildlife making choices. It took me a while to locate my misplaced book, but I finally put my hands on it and wanted to share one of these stories. The book is Seeds of Deception by Jeffrey M. Smith. Granted the original post is about domesticated chickens and egg shells, and this is about wildlife and GMO crops, but I think the common thread here may be an animals “sixth sense” so to say, and how they will accept eating one thing but reject another version of the same thing.

The following excerpt comes from page 45 in Seeds of Deception:

Wisdom of the Geese

There’s a farmer in Illinois who’s been planting soybeans on his 50-acre field for years. Unfortunately, he also had a flock of soybean-eating geese that took up residence in a pond nearby.

Geese, being creatures of habit, returned to the same spot the next year to again feast on his soybeans. But this time, the geese ate only from a specific part of his field. There, as a result of their feasting, the beans grew only ankle high. The geese, it seemed, were boycotting the other part of the same field where the beans were able to grow waist-high. The reason: this year, the farmer had tried the new genetically engineered soybeans. And you can see exactly where they were planted, for there is a line right down the middle of his field with the natural beans on one side and the genetically engineered beans, untouched by the geese, on the other.

Visiting that Illinois farm, veteran agricultural writer C.F. Marley said “I’ve never seen anything like it. What’s amazing is that the field with Roundup Ready [genetically engineered] beans had been planted to conventional beans the previous year, and the geese ate them. This year, they won’t go near that field”.

This last month,  we had an egg shortage, so settled for a couple flats of store bought white eggs.
The hens refuse to eat the white shells.

It could be as simple as the fact that if you're buying in eggs, it means that your chickens aren't currently laying.  

And if they're not laying, then their calcium requirements are much lower so they won't be so driven to search out and consume calcium sources.

Besides the lack of need for calcium it might be as simple as "Do you wash your eggs?"
If you don't wash the eggs that could be it, store bought egg shells are not only washed but sanitized so they would have a different smell to them.
But to determine this is the issue your hens would need to be laying regularly.