[GREENERS]

Wondered if anyone can help. I have been keeping free range bantem chickens successfully for 4 years. They are free range, happy and healthy. I originally had 4 hens and a cockerel. Two hens have died over the 4 years with no symptoms but as they were rescues I assumed old age. I have never lost one to a predator. I always treat for mites. This is not a mite issue. Currently I have one polish, one bantem and a silkie and the mixed breed hen in the story below. The 3 grown ups live in their own house. If anyone has time to read my story and give advice I wold be really grateful. It's getting me down losing my babies!

This year my silkie hatched 2 chicks. They were polish bantem crosses.
The first popped out overnight in the egg box and was dead by the morning so we assumed she sat on it by accident.
The second was a week later. So we moved her to our other hen house which is semi detached to the main house. It was given chick feed, water in a small waterer so no danger of drowning etc. It lived a week (was growing and looked healthy) then I found it dead in the corner under the straw one morning. I assumed it had suffocated in the straw.
So I bought two new 3 week old mixed breed chicks and put them in the same house on sawdust with the same water and chick food with grit. One died overnight. So we got another to keep it company. That also died within days.
So again to keep the mixed breed surviving one company, I bought two more babies. These were frizzles. The  mixed breed hen loved them and treated them like her babies. They have been happily living as a family for 3 weeks. The frizzles were growing and looked really healthy and out rummaging free most days with their adopted young mum.
Last night they were put away looking fine. This morning the baby frizzles were dead. the mixed breed is still alive!
There are no obvious reasons for death. No marks, lost feathers, bloating. Nothing. They look healthy, just dead. I live in the countryside. I can't see how any predators could get into the house. It's on paving slabs.
So I have now lost 6 chicks in the past couple of months. It's taking its toll on my kids who live the chickens and help look after them. Thanks in advance

[New shoot]

I have never raised chicks that young, but hopefully someone will be along soon with some more detailed advice.

One thing that crossed my mind was the weather. Paving slabs would heat up a lot in the sun and that would radiate into the coop. Perhaps heat stress has played a part.

If there are no outward signs of injury, it could be a disease, but it will be difficult to pin down the exact cause. I would move the survivor and the mixed breed hen into a temporary home and give the old one a very thorough scrub out and disinfect. A dog crate will do as a temporary home so long as you have it somewhere safe and in the shade. I wouldn’t buy any more chicks for now either. If the surviving one has a mother hen to look after it, it won’t be lonely.