Animal Reactions to UFOs

The reactions of animals during UFO sightings may provide clues to the nature of the phenomenon and how to conduct better research. So many sightings occur because the witness was alerted by a dog barking, or barnyard animals making sounds of alarm, but that aspect is usually just a brief mention in reports. Taking a deeper look, we find that all types of animals, from all around the world, share similar experiences to UFOs.
Animals have keen senses and don''t have an imagination, so their reactions prove that something real is happening. What can we learn from these animal witnesses?