I'm new here, but I've been reading a lot of posts to try to see if my question has already been answered. I'm also new at having bluebirds--we just put up the house this year. Each day, I see lots of activity at the house, with the dad feeding the babies. Pretty regularly, I walk out to the house to see if the mom is still in the house (so I'll know when to clean it out for the next nesters), and she flies out as soon as she hears me coming. Yesterday, I walked out to check on the nest for the first time, and the mom flew out when she heard me. I opened the house and saw three babies, who appear to be 9-10 days old, and two of them looked dead. One of them was barely moving its mouth open and closed. I got very upset, but then I read online that they can "play dead." Now I'm not sure if they were playing or not. Today, I've been looking at the house from afar and have seen almost no activity (the dad has flown up and looked in the hole a couple times), and when I walked up to the house, the mom did not fly out. I even tapped on it to see if she would come out. I'm so worried that they actually were dead! How does a beginner tell the difference between babies playing dead and actually being dead?