Why does my big chicks do this?

[Minah]

I can't explain but why does my big chicks crowd out in the corner and digging in the sand? You can see it in the video below

 

[Cazook]

what do you mean? it looks normal to me

 

[Aapomp831]

Why did yo my make duplicate threads?

 

[AntiqueB]

They're trying to dust bathe. Put a dish of some fine dirt or sand, without rocks or twigs in it, and they will flap around in there, bathing.