We're stumped! We successfully had a hen set her own eggs last year inside a pen. Nothing bothered them. This year, something that could climb a wall and go through a 1 1/2 in. space got inside and killed our 10 baby chicks. Then we had another hen setting on 14 eggs and we decided to move her inside to prevent another catatrosphe. She didn't have 14 eggs anymore, only 7 were left (we did, during her 21 day setting, find 2 hollowed out shells). Of those 7, none hatched...which we will assume were not fertilized. We now have another hen setting, and she started with 13 eggs, down to 12 yesterday & only has 10 now. All the other occurences seemed to be at night. But, with this hen setting now...she is locked up tight at night. So the thief is stealing them in the day time. If they are being eaten or stolen at night, then the predator must fit thru a half inch space and eat everything without leaving a trace. What is it? We've spent hours online researching predators and can't figure out what it might be. Meanwhile, we put one of our dogs inside her pen...which is a pen large enough for the dog and her nesting house...which gets locked up at night. FYI: Our dogs are the protectors of chickens, they wouldn't harm the mama hen or steal her eggs...so that's our only answer for the time being. They are the reason coyotes stay away from our house.