I have one male and one female peking duck. I have about 60 chickens. I think my male duck is killing chickens by trying to mount. I found one dead several days ago wedged underneath a wood box, like it was trying to get away from something but no puncture wounds, comb and ears purple, a definite mystery. Then a couple days later I caught the male duck trying to mount a hen, holding onto the neck and trying to mount. Now I've seen the duck do this many times, and when I'm around, I knock him off, but I've never had any fatalities from this. I've never had any chicken deaths that weren't obvious of what caused it, like a sickness or a neighbor dog. In this case, when I knocked the duck off, the chicken still laid there and didn't hop right up, and not like they do sometimes when they're staying in the submissive position, but laying down sideways and the comb and ears purple and she was limp, toes curled under. But I picked her up, separated her for a day and she was fine by the next day. Then yesterday, found one laying over in some hay, not moving, distressed, but not dead and when I separated it to see if it recovered, it was back to itself within 20-30 minutes. And then finally today, I went out in the afternoon and found another dead hen blue comb and ears. Our LGD was close by but just watching. She did that when owls got some of my guineas, like, guarded the body until I removed it. Again no puncture wounds or really missing or wet feathers. It was a nice big fat healthy hen. So I feel like I'm 97% sure it's the duck, but I just wanted to see if this is more common than I was aware, and thereby making me 100% sure. I have since moved the male and female duck to a back pen, to the "goat" pen, where only a few of the "wily" type chickens go, not the docile red hens. I doubt they'll be caught by the duck. But if I find a dead chicken back there I guess I'll know for sure!!! Just wanted to see what y'all's thoughts on it were. Thanks.