So sorry for your loss. It's hard to say what predator it might be. I could be one of many. My first thought would be to put up a camera and see what is lurking, then once you know what you're dealing with you can make a plan but until then lock up your remaining birds. I have several game cameras up around on my property. I have some mounted on post so I can move them around. I see a predator most every night, when they roam here, on at least one of my cameras. I love my cameras. Good luck...