Before you get worried, we'd like you to know that no owls are harmed in the making of fine California wines. In fact, they get paid well — in rodents.
Rodents like to eat grape vines, and Barn Owls like to eat rodents. Many Napa Valley wineries control rodents by putting up nest boxes to establish Barn Owl populations. Researcher Sara Kross from the University of California Davis says that more than 99% of prey items in barn owls’ diets on the farms she studied were agricultural pests — mice, voles, and pocket gophers. Fewer of these pests means easier growing for grapevines.
Welcoming Barn Owls allows wineries to reduce or eliminate the use of rodent poisons. It's important to note that, if poisons must be used, they should be used with care, since an owl that eats a poisoned critter will ingest the poison, too.
Intrigued? You can read more about Kross's research here, including where to get nest boxes of your own.