We've been withholding food when they are out, but we have been offering them treats to reinforce behaviors we appreciate. Maybe we should re-think that...or find that one treat they love and only get when they have gone in.
Unrelated question: What about temps and, more importantly, temperature swings? My wife likes her studio warm--around 70F, but she usually lowers the thermostat to around 60F when she is not in the studio. Obviously 60F is plenty warm for the birds, but are the 10F-temperature swings something we should modulate?