I never knew

https://www.fieldandstream.com/do-deer-eat-meat/

Everything needs protein.

Animals figure out easy ways to get it.

Decades ago as a boy scout, we were camping at their "high adventure sea base" down in the Keys. We were just beginning our 6 nights camping on a small island and having a great time.

The mood changed dramatically when we watched a Key deer enter camp, take a steak off the table, and walk away like a boss. I mean, who wants to be trapped on a small island with meat eating deer!?! We knew we had to watch our backs from that point on.

I enjoyed seeing the key deer. Steve was my favorite. We enjoyed Munson, not the canoe trip as much.

I have seen horses and deer eat small birds

More than likely it is for the calcium. They will chew on drop antlers as well.

At one of the zoos I worked at, the antelopes liked to jump on rats, smash them, and then eat them. It was pretty funny to see people watching that

Back in the 70's the Wonder Cave over around San Marcos had an incredible meat eating deer herd. Damn things would trample you for a chicken leg.