Bruce,

This website suggests that they migrate:
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1144&context=icwdm_usdanwrc

It also says:
"Most of the interior populations are located from the Great Lakes west across the northern prairies of the United States in Canada."
Considering that you're in the "Upper Central Midwestern Great Plains," that puts you in their neck of the woods.

P.S.- Don't tell the cormorants on the Gulf Coast that they're the minority. They sure don't breed/act like it.

"Only after sorrow's hand has bowed your head will life become truly real to you; then you will acquire the noble spirituality which intensifies the reality of life. I go to an all-powerful God. Beyond that I have no knowledge--no fear--only faith."