Chick's clustering to one side of enclosure

[Eggrigg]

I have been stumped by some recent chick behavior and was hoping for some guidance.

My chicks hatched April 1st, and I had them with an infrared heat lamp and EcoGlow brooder. (I will refer to their entire brooder space as the enclosure, the EcoGlow as te brooder to avoid confusion). They used both heating sources interchangeably, and as the 1.5 week mark hit, they started using the brooder more often. I have two temperature gauges: one on the cold side of the enclosure and one that I use to monitor both heating sources. I have read up on sources about the temperature they should be at, and the brooder stays around 80 degrees but the heat lamp closer to 90. So, since they are entering their third week I removed the heat lamp yesterday. They all stayed happily under the brooder all night and even seemed a little on the colder side. I put a blanket as the base where the brooder is to retain some warmth, but raised the legs up a little so it wasn't too hot or stuffy. I checked the temperature three times today and it has maintained at 80.

Suddenly however, the chicks started clustering into a tight bundle on the cold side corner. Every single source I read says they do this when the heat source is too hot, but the entire enclosure is cooler than it has been. I have monitored the temperature of their heat source closely enough that it doesn't seem to make sense. The only different is I removed the heat lamp which made me believe they would all use the brooder more often. Any thoughts? I am completely out of ideas.

Here is a photo for behavior reference.

Thank you!

 

[cavemanrich]

When chicks are clustered together, it usually is an indication that they are cold. and stay warmer by being bunched.
The accepted guideline on temperature is to reduce by 5°F each week. So at end of week one,,,,,,,,,,,,,,, 95°
week two,,,,,,,,,,,,,,,,,,,,,90°
week three,,,,,,,,,,,,,,,,,,85°
week four,,,,,,,,,,,,,,,,,,,,80°
This tells me that your chicks were enjoying the heat lamp, and venturing under the EcoGlow at will.
You raised the height of the brooder heater, and it just isn't sufficient heat for their comfort.
I suggest you reinstall the heat-lamp again for another week, and try to lower the heat output weekly, by raising the height of light above enclosure.
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,