The most common owls in the world are also in the Galapagos Islands and are considered subspecies that only occur in Galapagos, so one could almost say they are endemic subspecies.
The Barn Owl subspecies is the Tyto alba punctatissima and can be found on Isabela, Santa Cruz, Fernandida, Santiago, San Cristobal, Pinta, and maybe also in Floreana. On the main Islands of Santa Cruz, San Cristobal, and Isabela it is found near the garbage dumps where food (rodents) is plentiful. Driving at night near the dumps is a good way to find it.
The Short-eared Owl subspecies is the Asio flammeus galapagoensis and can be found on Isabela, Santa Cruz, Fernandida, , Santiago, San Cristobal, Floreana, Marchena, Española, Pinta, Santa Fe,Pinzon, Tower, and Darwin. I have only seen this bird near wide open “fields of lava” where I suspect it is easier to see their prey.
If you have not visited the Galapagos Islands you may want to read this report before you book a tour: Birdwatching Galapagos Islands