Why could it be that my chickens all pile in......

. First of all, how old are they? If they are full grown, which I can't imagine if they are all fitting in one nest box, then they need to be taught how to roost. If they are young, and not laying yet, I would block off the nest boxes at first. At night, when it's dark, go out to the coop and place them on the roost. Once there, they won't move because they can't see. You may have to do this for a week or longer until they get the hint. I love chickens, but sometimes they are not too bright, I had some I got at 2 months old, and it took almost 2 weeks to train them to use the roost. My guess is they are doing this for comfort. The nest box is nice and cozy, that's probably the main reason. But you need to teach them to roost, and that the nest boxes are only for laying eggs!

 

Piling is usally a sign that your chicks are cold and smothering could happen depending on the number of chicks. I brood in a circular brooder which cuts down on corner pile-up should the bulb go out. Fright also makes them pile, but they're all jumping and bouncing there is litle chance of smothering, maybe an injury though.

 

Quote:Do they normally sleep on a roost?
Put a nightlight out there & see if they stop going in the nestbox.

 

Mine did that for a little while and then they all figured out the whole roosting thing and it worked out fine.