Looking for answers from chicken experts. I lost four Rhode Island chicks in the past 10 hours (when I last checked them). Each sustained injuries under the wings, back, and neck, and one underbelly, but none "eaten." I see no obvious evidence of an intruder. They were roughly a month old, sharing a 10'x10' pen with New Hamphires and Plymouth Rocks. All the same age and purchased together. Is this "unfriendly fire"? Are they killing each other? Advice or opinion?