Dogs usually won't carry away the bodies. They'll just leave them where they killed them. Sounds to me like you had a fox attack. Yes, they will take more than one bird at a time. I lost 7 in one attack and 9 in another. All I found of the missing birds was piles of different colored feathers throughout the yard. You could see where the attacks started, and how the fox continued after the birds across the field into our front yard. It was like the chickens came to the house for help. Both attacks were daylight attacks but, a fox is a 24hr a day threat. A fox will kill as many as he (Or she) can, and then carry them away and cache them somewhere. I use to freerange my birds, but after the daylight attacks, or course when I wasn't there, I now have a 100X100' area around their coop surrounded by Premier's electrified poultry fence. They only get out of the fenced area if I'm there with them.
Jack
Jack