Why are my chickens huddling?

[melodyrg]

Lately my 6 week old pullets will come inside the coop and huddle together on top of each other in the corner nearest the door. Does anybody have any idea why they'd do this? I've only had them in the coop for 2 weeks or so and the run was just added last weekend. Thanks in advance, oh and the chicks are fully feathered but I found that sometimes turning on the heat lamp in the coop makes them spread out, but I can't possibly see how they could be cold with 50 degree weather at night.

 

[ChickenRaiser95]

maybe the like ti warmer... just have the heat lamp on, they also might just like to snuggle eachother...