I have 3 hens about 17 weeks old. Woke up this morning to two of them dead. No signs of injury, no way of a rodent getting in. One was in the nesting box, the other on the hut floor. One had a bit of a grey greasy bottom but that's about all I can tell you. Their hut is completely clean, they have fresh water and good food. Please can someone offer up any explanation? They were really healthy and happy yesterday. We are very sad and our remaining bird is all alone now. Please help?