barn owl

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A predatory nocturnal bird (Tyto alba) having a white, heart-shaped face, buff-brown upper plumage, and pale underparts, often nesting in barns and other buildings.

from The Century Dictionary.

• noun The common white owl, Strix flammea or Aluco flammeus: so called from being often found in barns, where it is useful as a destroyer of mice.
• noun plural The owls of the barn-owl type, genera Strix or Aluco and Phodilus, which differ so decidedly from all other owls that naturalists now consider them types of a distinct family. See owl and Aluconidæ.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An owl of the genus Tyto, often having a white face and commonly found in barns and other farm buildings.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun mottled buff and white owl often inhabiting barns and other structures; important in rodent control