To the original question yes, a dog can kill a bird without leaving a trace. Our female killed a baby robin on our way down to do chicken chores yesterday. I turned around when I heard a squeak saw a bird in her mouth, told her to LEAVE IT! She dropped it, but it was too late and it died. I tossed the poor thing into the bush and told her to l her to leave it again and we went down to feed and water the chickens. The difference between the chickens (so far) and the robin is that the chickens are "mine" and I have corrected her from the beginning for even looking at them the "wrong way". If she looked at them and started to drift into that predatory fixation I would snap her out of it. Some times that ment a growl "mine" , sometimes it went a poke to the shoulders and a "Mine!" And a couple times it involved a swat and a "Mine!" To break her out of that "Gotta catch it, gotta squeak it! GOTTA GET IT!" Mind frame. I'll never trust her alone with them, however we have made huge progress and today she was actually allowed inside the coop while I handed out treats. A big deal considering the chaos and excitement that's involved with treats. She was being so good in fact that in tossed her a treat and... Oops the chickens mobbed her for it! She gave up the treat to the chickens and, figuring I had been lucky, I didn't toss anymore at her feet. She got special treats after that for sure!