Strange Small Chick: Why hasn't she grown?

[HistoryChicken]

Hi,
We have a couple of chicks that one of our hen's raised. They are 12 weeks old now and one of them is really small. Her feathers have developed properly either. She is an AraucanaXBarred Rock. The other one is an AraucanaXAndalusian. Don't if the second one is male of female.

Here is a picture of them together.

Here's a close up.

Then a couple of picture showing the feather problem.

Her mother is a perfectly normal Barred Rock. Her father never got feathers on his shoulders properly, but he's the other one's father too and there's no problem there. By the way he was Greyish white in case that's that useful

The two chicks get on pretty well. The little one, Abby, has been staying inside the chicken house as she gets cold outside. It's the middle of summer here but the weather has been unusually cold. we have the fire on in the house at the moment. She has been trying to snuggle under her bigger sibling since there foster mother abandoned them a few weeks ago.

Her's one more picture of the two of them

Any idea what's the matter with her?

 

[dawg53]

I suspect that it's a genetic issue. Just as long as she is eating and drinking normally, I wouldnt worry too much.
However, there are plenty of other reasons why birds can be runts; malabsorption, reovirus, nutritional deficiencies and so on.

 

[HistoryChicken]

Thanks for that.
She is eating and drinking normally. She seems to get cold easily though. Do you think that she will eventually grow up and start laying when she is older?

Is there another thread where it would have been better too ask this question?