I have one pekin duck that has lived peacefully with my flock since we started with chickens last spring. Our original flock consisted of the duck and three roosters. The remainder are hens from last year and pullets from earlier this year (16 weeks). About ten days ago I found one of my roosters dead. No signs of injuries, so I figured it was the heat even though there was plenty of water and shade. It had been in the upper 90s for a couple days. On Sunday I noticed another of the Roos was missing a few feathers from the back of his head. I also noticed that the duck was chasing him a little. The roo jumped on a perch, which the duck can't, and seemed fine. The next day I found him dead with more feathers missing from the back of his head/neck. So, can ducks become agressive towards chickens they've lived with for well over a year with no problem? I'm looking to rehome the duck, but I want to make sure it's a good home and not for the wrong reason. Thanks.