No doubt in my mind that they can take a full grown deer. Many people try to invision coyotes taking deer such as a mountain lion would, but running it down and killing it quickly, but they will first work the deer to exhaustion to weeken it, then they will take it down. I've seen coyotes take full grown cows too, and that's how they did it, wore her down to exhaustion, then they start eating while it's still a live.