I have been watching this for long enough to come up with a decent understanding of what to look for when an unknown disturbance for someone is likely a Great-horned Owl.
First think I notice is that when chickens can see the owl they make a characteristic alarm call.
The next thing I look for is how the roosting birds posture. The chickens fluff up holding tail as shown. They will often hold neck extended and roughly at a 45 degree angle below horizontal. For seem reason the chickens hold tight to roost when owl comes until owl almost contacts them.
First think I notice is that when chickens can see the owl they make a characteristic alarm call.
The next thing I look for is how the roosting birds posture. The chickens fluff up holding tail as shown. They will often hold neck extended and roughly at a 45 degree angle below horizontal. For seem reason the chickens hold tight to roost when owl comes until owl almost contacts them.
