Someone asked on another list years ago asked why birds don't get their temperature checked. The answer I believe was that birds don't maintain body temperature nearly as consistently as mammals do. It can vary by a couple degrees and there are sometimes species differences. Mine often feel like their beak or feet are warm. Usually because they've been sleeping with their feathers puffed up over their feet and their beak tucked under. Sometimes it just feels warm because I'm cold. I tend to go more on behavior than temperature. I look at poops, weight, food consumption and if they are fluffed up and sleeping more than usual or not.
Melissa