One Chicken Dead - Breast Down - No External Signs of Injury

[TheFarmerInDale]

I had a friend watch our gals for 4 days this week. She said she had no problems.
Yesterday we moved the ladies to a new grazing area, letting them free-range for the day while we moved them.
One of the hens did not make it to the coop last night, and I figured she'd be gone come morning - as we have a bit of a coyote problem in our area. But I saw her strutting around the morning, happily still free-ranging.
I opened up the coop this morning and didn't notice anything off (though still rubbing the grogginess from my eyes at that point).
I come back less than an hour later to find this 2 year old gal dead, breast down, with no signs of struggle or bites.
The coop is in good order, no holes anywhere except a slit where a young snake could squeeze through.

I'm about to go do an autopsy. Is there anything I should look for?
Any and all help on a diagnosis would be appreciated greatly!

Circle of life. Just another chance to learn something.





EDIT:
Here's the link to the autopsy. I hope it's not too offensive at times.

 

[Liz2]

Did you ever find out what might have happened? I let our chickens out this morning and a few hours later I found a RIR sitting on the floor like she was nesting but she was dead. Stiff with her eyes closed and feet under her.

 

[aggiemae]

We have had this happen a few times between 2 and 2 1/2 years, always with larger breasted breeds like Orpingtons. Once I was tossing scratch to the flock and one died in the few minutes it took me to fill the waterer bucket.

Vet says they are more meat birds then egg layers and short lived, their hearts just stop. I just avoid those breeds.