I think the predators do not require prior experience with a potential prey item for them to give it a shot. The potential prey simply needs to provide sensory stimuli that predator can detect and indicates item is not too large or not worth the effort. If stimuli appropriate then the predator investigates. A novel prey item will not be as quickly attacked unless by reflex. The predator may be faced with a learning curve if prey has defensive measures predator is not familiar with. Generally chickens have low defensive capabilities so even though they may present a novel situation to some predators, they will quickly be found to be easy and properly sized and in predictable locations to be worth repeated effort by many predators.
