Bull, E. L., and J. R. Duncan. 1993. Great Gray Owl (Strix nebulosa). In The Birds of North America, No. 41 (A. Poole and F. Gill, Eds.). Philadelphia: The
Academy of Natural Sciences; Washington, D.C.: The American Ornithologists’
Union.
Cannings, R. J. 1993. Northern Saw-whet Owl (Aegolius acadicus). In The Birds of North America, No. 42 (A. Poole and F. Gill, Eds.). Philadelphia: The
Academy of Natural Sciences; Washington, D.C.: The American Ornithologists’
Union.
Duncan, J.T., and P. A. Duncan. 1998. Northern Hawk Owl (Surnia ulula). In The Birds of North America, No.356 (A. Poole and F. Gill, Eds.). The Birds
of North America, Inc., Philadelphia, PA.
Hayward, G.D., and P. H. Hayward. 1993. Boreal Owl (Aegolius funereus). In The Birds of North America, No. 63 (A. Poole and F. Gill, Eds.).
Philadelphia: The Academy of Natural Sciences; Washington, D.C.: The American Ornithologists’
Union.
Houston, C. S., D. G. Smith, and C, Rohner. 1998. Great
Horned Owl (Bubo
virginianus). In The Birds of North America,
No.372 (A. Poole and F. Gill, Eds.).
The Birds of North America, Inc., Philadelphia, PA.
Johnsgard, P. A. 1988.
North American Owls. Washington, D.C., Smithsonian Institution Press. 289 pp.
Parmelee, D. 1992. Snowy Owl (Nyctea scandiaca). In The Birds of North America, No. 10 (A. Poole, P. Stettenheim, and F.
Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington, D.C.: The
American Ornithologists’ Union.