What can I use to provide heat for my quail?

[shelleyd2008]

I have 16 button quail that are getting a new (bigger) cage. When it arrives, they will also be going outside. I know I need to cover the cage, but what can I use to provide heat without having a light source?

 

[chevydmax04]

I have a 500W infrared heater that I use when it gets below 20, for 20 and above I have a 100 W red heat lamp. Also my coop is insulated and it stays toasty warm even on the coldest of nights.