I have seen the raven/crow stealing eggs twice - egg in its beak!
At one stage, the local ravens/crows came to check the nests every morning to see if there were some eggs to steal. They aim to steal my chickens eggs from the nests before the eggs are collected.
I have been vigilant but the hens are free ranging and I can't be in the yard all day long. Luckily, the local birds hate those corvids, I know one is nearby when the neighbourhood birds alarm ring berserk.
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This was an fake plastic egg that I had placed in the nest, the holes were the 'courtesy' acts of local crow/raven.
Nowadays, they know not to steal the fake but only go for real. I use broom to chase them away whenever I sight one.