My chickens are eating a lot of mulberries. Purple poop everywhere. They have dropped from an average 6 eggs a day down to 3. Are the mulberries doing this or something else?
I agree, probably something else.
I'll get this out of the way first. Are they molting? If you have mulberries it is not your normal molting time but many other things can trigger an out-of-season molt. I doubt if it is this, but are you seeing feathers flying around?
A very common reason for you to think they are not laying is that they are hiding a nest on you. That happens a lot.
Another common reason is that something is getting the eggs. Most critters that take eggs leave some kind of sign, bits of eggshells or wet spots. A snake does not, it swallows them whole. A snake typically eats some eggs then disappears for two or three days while it digests them, then comes back for more. A five feet long black snake would eat four eggs and then disappear for a few days before it came back for more. So if it is an everyday shortage it is probably not a snake.
Canines swallow the eggs whole. I'm not sure where you are in the world so I don't know what canines you might have to consider. In North America coyotes or foxes would probably be more interested in your hens than the eggs but dogs can eat eggs and not bother your hens. Does a dog have access?
A human does not have to be a stranger. Some people consider doing something like this to be a great practical joke.
So what can you do? If you can lock them into a coop or a coop and run where they are not roaming looking for mulberries you may be able to see if any strange eggs show up. That could mean they cannot get to a hidden nest or you may have locked an egg eating animal out. You could put a mark on an egg and leave it down there to see if it disappears. If it does disappear you know something is taking them.
Or it could be that they are just taking a break. That can happen.
Good luck. This stuff is sometimes frustrating in solving.