The Barn Owl
The Barn Owl (Tyto alba) was introduced to Hawaii in April, June and October 1958 to control rodents. A total of 15 birds were imported from California by the state Department of Agriculture and released at Kukuihaele on Hawaii Island. Over the next five years, an additional 71 owls were introduced on Kauai, Oahu, and Molokai on Molokai Ranch lands. Nowadays the barn owl is found throughout the main Hawaiian Islands, including offshore islets such as Lehua near Kaua‘i.
They have light grey underparts with numerous fine dark lines and scattered pale spots on the feathers. There are buff markings on wings and back. Feathering on the lower legs may be sparse. The heart-shaped facial disc is white with a brownish edge, with brown marks at the front of the eyes, which have a black iris. Its beak is off-white and the feet are yellowish-white to brownish. Males and females are similar in size and color; females and juveniles are generally more densely spotted. Barn owls can be distinguished from pueo by their primarily nocturnal habits, rounder faces, and lighter colouring.
Though considered a rodent specialist throughout continental North America, barn owls in Hawaii have been documented preying upon multiple avian species and may pose a significant threat to nocturnally active seabirds. Seabird predation by barn owls has been documented on offshore islets, the coast of the main islands, and in montane forests where they are known predators of endangered Hawaiian petrels (Pterodroma sandwichensis) and threatened Newell's shearwaters (Puffinus auricularis newelli). Seabird mortality due to barn owl predation has been repeatedly documented on Maui Island on wedge-tailed shearwaters (Puffinus pacificus), on Lānai on Hawaiian petrels, and on Oahu's offshore islets on Bulwer's petrels (Bulweria bulwerii). Loss of adult petrels to owls is significant. Predation on breeding adults leads to reduced breeding success, and owl predation at all life stages prevents successful implementation of planned recovery actions for the species.
A barn owl, which is an invasive species in Hawaii, flies away from the burrow of an endangered petrel. The following morning the depredated petrel was found in that location, and the pattern of flesh removal is consistent with owl predation. Photos by Hawaii Department of Land and Natural Resources Division of Forestry and Wildlifeof (left) and USFWS (right).
Because barn owls will breed at any time during the year, and depending on food supply, they can reproduce up to 2 times per year, they are able to increase rapidly in a relatively short period of time. Barn owls likely compete with the native pueo for introduced rats and mice and could potentially be limiting their population. Techniques for barn owl removal including trapping and shooting and are regulated under the Migratory Bird Treaty Act and Migratory Bird Depredation permits.
References.
Mostello, C. S. 1996. Diets of the pueo, the barn owl, the cat and the mongoose in Hawai‘i: Evidence for competition. M.S. thesis, University of Hawai‘i at Manoa, Honolulu
Kīlauea Point National Wildlife Refuge Comprehensive Conservation Plan. Chapter 4 Refuge Biology and Habitats
Barn owl sounds from http://www.xeno-canto.org/