My first thought was also that the feathers on the ground belong to your rooster. There aren't enough feathers there that you would notice him missing any. I thought they were your rooster's feathers because in the photo he appears to have a white undercoat, and also you later said he was standing guard alone. The one black and red feather appears to match his tail or wing feather colors. Those definitely look like chicken feathers to me, so carefully check over your rooster and all hens with red outer feathers and white undercoats. Feathers easily hide and cover wounds, and could become infected before you notice a problem.