West of the Mississippi from Canada to Central America lives the Burrowing Owl. These small, brownish tan-colored owls with bright yellow eyes are the only raptors in North America that live underground in burrows they dig themselves or usurp from a ground squirrel or tortoise. In open habitats like grasslands and deserts, they eat rodents and bugs. Standing about 10 inches high with a wingspan of maybe 2 feet and weighing around 7 ounces, the Burrowing Owl is slightly larger than the American Robin.
The extinct Giant Cuban Owl resembled the Burrowing Owl in shape, but stood 3 feet 7 inches tall and weighed about 20 pounds! Its relatively small wings probably made it flightless. Ornimegalornyx, the scientific name of this largest owl that ever existed, means “bird with big claws.” Strutting around the forested islands of Cuba until it died out 6000 years ago, this giant owl hunted animals as large as stocky Caribbean rodents and small capybara, the largest living rodents. Like other ground-dwelling birds, the Cuban giant was probably a good runner, and it very likely ran its quarry down before dispatching it with its powerful talons and beak.
Asio ecuadoriensis, another ancient owl, lived in Ecuador until about 10,000 years ago; it was more than 2.3 feet tall with a wingspan of about 5 feet. A cave-dweller , the Ecuadorian owl was unusual in that it ate not only the usual diet of rodents and rabbits, but other owls, appearing to be an owl-eating specialist.
I am sure you are familiar with the extant Barn Owl (Tyto alba), one of the most widely distributed species of owl in the world and one of the most widespread of all species of birds, subdivided into 28 subspecies. The Barn Owl is found almost everywhere except for the polar and desert regions, Asia north of the Himalayas, most of Indonesia, and some Pacific islands. For the scientifically curious there’s an interesting paper about the evolution and diversification of Barn Owls you can read.
About 30,000 to 10,000 years ago there were also giant Barn Owls, about twice the size of today’s species. Tyto robusta and Tyto gigantea lived on Monte Gargano, an island when the sea levels were higher 20 million years ago and now a part of Italy. Tyto robusta was a bit smaller than Tyto gigantea, so they ate different sizes of small mammal prey and were able to coexist.
There was also a giant Scops Owl, Otus murivorus, on Rodrigues Island in the southwestern Indian Ocean, which only went extinct in the late 18th century.
Note that most of these large birds lived on islands or in isolated habitats. It’s easier for birds to get to islands than large mammals and without mammalian predators, birds take their place and grow large and predatory, and are often flightless.
A lack of large predators on islands has led to interesting and even bizarre adaptations of bird forms besides giant owls, such as the Kiwi, Kakapo and moas of New Zealand, the Dodo of Mauritius and one of my favorites, the Kagu of New Caledonia. Problems arise, however, when mammalian predators such as dogs, cats, and humans, colonize the island and decimate the birds which have no defense against the invaders.