I think you need to move it around periodically for it to be convincing. I know there are ones out there that also have a motion sensor in them so they will hoot when something moves around close to it. That may help too.
We put one near the garden to scare the little birds away from my corn & veggies. The little birds used it as a landing site and pooped all over it. The chickens were NEVER scared of it. The hawk still circled overhead eyeballing my chickens.
A motion sensor that hooted might've had a more positive impact.
I have one that was given to me and stuck it on a post. Well the hawks and chickens could care less about it, but it took my mare a 1/2 hour to realize it wasn't going to eat her. I couldn't stop laugh she would get about 2 feet away from it snort, the owl would move a tiny bit from the wind and she would turn tail bucking and running. She can be such a goof.
I bought one a few years ago when I still lived in St. Louis. Got it to get rid of the dang pigeons. Didn't work at all. They would knock it off the rafters onto the porch, so I tied it on there. They would sit on top of it and peck it and poop on it. I had a problem with them for 10 years. Low and behold the thing that finally made the flying rats disappear was 2 hawks that took up residence in a tree in our backyard! A rarity in such an urban area. I still have my house there and was down last week. The hawks are still hanging out there and there are still no pigeons. I guess it's all relative. I loved the hawks in the city, but loathe them here in the country. They are the size of prehistoric birds. I have never seen such huge hawks and eagles in my life. They are quite a menace to me and the girls. Maybe I can try to trap the bad boys and ship them to my house in St. Louis! LOL.
I'll try bringing the owl up here and see if it does any good. I'm betting not. These hawks and eagles have actually swooped down on my german shepherd. You would think with his barking and chasing at them that they wouldn't bother with something as big as a german shepherd. But, I've learned to put nothing past these flying wonders. They are just so very intelligent and spend their days trying to outsmart me. They usually win!