[dancelady]

I think it was the heat from the heat register adding too much heat and drafts to the birds. If they were not adapted to it, it could easily have overcome them and quickly wiped them out. Being right over a heat register is a very bad thing and is recommended not to be used for birds. I can just imagine what happened, the birds got overheated. This is what killed them. You must not use that location any more -- although the other birds have not shown this yet, if it gets hot there, another bird could also get heat exhaustion, even if higher up. I would move those birds to another location and turn off the heat right now!