Duck postmortem, filled with grit? GRAPHIC PHOTOS

[M-machine]

We had a duck in my workplace flock that went downhill very quickly over the last week and died. I did my first amateur postmortem on her to find that her gizzard was very large and totally stuffed with gravel and almost nothing else. In hindsight I did see her out by herself in the field meticulously eating something, which I now assume to be copious amount of gravel? I’m wondering if this was a behavioral issue or if there’s a reason she ate so much grit? The only other thing I noticed was that she had almost no body fat which I attributed to nutrients being hard to process when you’re full of rocks. I work under a vet tech who is also bamboozled, and I am by no means a professional when it comes to medical exams so I’m wondering if anyone else has any experience with this?

I took necropsy photos of her which are *VERY GRAPHIC*

Thanks in advance!