The Raptor Center: Boreal Owl - Facts about the identifying traits, range, habitat, nesting, and diet of Aegolius funereus. - http://www.cvm.umn.edu/raptor/info/borealowl.html
Boreal Owls / Tengmalm's Owls - Boreal or Tengmalm's Owls - descriptions, photos and sounds. - http://www.owlpages.com/species/aegolius/funereus/Default.htm
The Boreal Owl: A Superb Hunter - An article by Tomas Johansson about the Boreal Owl. - http://www.outdoor.se/english/artiklar/uggla/