Apologies for the poor job with cut and paste, the citations should read:

Livezey, K.B. 2009a. Range expansion of barred owls, Part I: Chronology
and distribution. American Midland Naturalist, 161(1):49-56. Available
online at http://www.bioone.org/toc/amid/161/1 (August 8, 2010).

Livezey, K.B. 2009b. Range expansion of barred owls, Part II:
Facilitating ecological changes. American Midland Naturalist,
161(2):323-349. Available online at http://www.bioone.org/toc/amid/161/2
(August 8, 2010).

The abstract posted previously was from Part II (Livezey 2009b).

And of course I meant "caused by post-European settlement" since humans
were already on this continent and were already modifying the environment,
as is discussed in the paper.

Janet Millard
Leavenworth, WA