How warm is it where you are located right now? Sounds like they don't need the heat anymore. My cayugas only needed heat their first week of life, after that they were too warm with the heat lamp on and would pant. I'd do as Amykins suggested and turn off their heat lamp for awhile and see what they do. If they start to huddle together and look cold, then they still need the lamp and maybe you can move it up higher above the brooder so it doesn't get quite so warm in there. Otherwise if they seem comfortable without the heat lamp, then it's time to just remove it.