I definitely do believe that certain pets should be kept separated from each other. Dogs and chickens are natural enemies, yet at times a dog will be protective of 'his' flock, assuming that he's been well trained and watched carefully. One must use discretion when allowing certain pets to roam freely together, and it's best that those pets be monitored during their interactions. A much better idea for chickens is to have a small flock of geese nearby as they tend to act as watchdogs, honking loudly and rushing at any strange animals that might pose a threat to the flock. In this way, I was able to keep chickens, ducks and geese together in the same run for years, without losing any birds to predation. Chickens themselves often cause the most damage to each other as they will spot something red, such as the wattle of another hen, and peck at it for hours until the poor victim is either gushing blood from multiple wounds or lying there dead. So in some cases, even when the pets are related, or of the same species, they still attack and kill each other. Pets of any kind are capable of hurting or killing each other if they aren't kept under control from time to time. I firmly believe that pet birds and cats shouldn't be allowed near each other without human monitoring, as some things are just common sense.
