I'm not sure what is digging under the fence, but this is three days in a row. The first day I noticed the hole it was beside one of the fence post and we had a heavy rain - since we had just built the pen I figured the rain had settled the dirt so I filled in the hole. All of the chicks were okay so that was my assumption. The next day I notice a hole in the same spot but again we had rain and the chicks were okay, but I was beginning to wonder. I was telling my husband about it and he wanted to know if I had packed the dirt down tight when I refilled. For the first evening we had no rain and I go out and there is the hole again in the same spot. It's big enough for a cat or possum or rat - but all the chicks are fine. This morning I am going to lay down wire on the inside and stake it down with tent stakes. It's the only fenced area that is outside of where our dog can reach. All other three sides are on the interior of the yard - this is on the privacy fence to the back - we left a wooded barrier to the back of our fence just for sound and privacy - it belongs to us - not sure what might be coming in that isn't bothering the chicks.
Do you leave the feed out at night? Skunks would do this where I am. Come and feed so I didn't worry about them then after a year a large male started to take chickens. Remove feed at night and if the chickens don't have a secure coop then hard wire mesh along the perimeter laid flat will stop them from digging in.
There is always the possibility that it I something that hasn’t bothered the chicks yet. Sometimes critters that can and do take chickens don’t take them at the first opportunity. They may be going in to get the chicken feed or something else in there. Many critters would not bother digging but would probably go over the fence instead. Raccoons, bobcats, members of the weasel family, and possums immediately come to mind. But each predator is different. They don’t all read the book and do what they are supposed to do. That still leaves a lot that would dig underneath a fence. I could easily see a skunk or something else going in there for the chicken feed instead of the chickens. It could be chipmunks or ground squirrels. Lots of things like chicken feed. It could be a groundhog going in there for its own reasons. It could be a lot of things. You’d be surprised by how small a hole many larger critters actually need to get under a fence. Now that it has quit raining, have you looked for tracks or scat? Either one can help you determine what it is. Rake the dug ground flat and see what shows up. Maybe even scatter some flour to help you get good prints. When you lay that wire make sure you attach it to the bottom of your fence. I’m not sure if the fence is wire or wood, but something could squeeze through an opening between the fence and that wire if it is not attached. Good luck on identifying what it is. It’s hard to deal with an unknown.
Thanks for the suggestions - I do leave feed out at night - I will stop that - they do have a secure coop and we have the pen completely enclosed, including wiring on the top. On the bottom we began with heavy gauge, coated chicken wire, but found our dog could get through. We left the chicken wire and went over the top of it with the 1/2" hardware cloth under the coop and 1" hardware cloth around the bottom four feet. We left the regular chicken wire above that and ran 2x4's horizontally the entire length and ran additional 1x4's as slats. We used shutter boards over the fence and laid concrete pavers in front of that. On the side where our dog spent too much time looking at the chickens, we took 3 foot hardware cloth and stretched across the ground and staked it down with 18 inch metal tent stakes and then covered it with a layer of dirt. - we ran hex wire on the ground on the other side - the third side we have the concrete pavers. The only side we didn't secure from outside the fence with some type wire or pavers was the privacy fence and that is the area where what ever is coming in.