Anyone notice a pattern in the above maps? I do. Every other year, a visible movement south and east is quite pronounced,
save for the Red Crossbill. CBC's run the last two weeks of December and the first week of January. For years where the
December CBC is an odd year, Northern finches make a greater movement to the south and east than when the December CBC is
an even year. What causes this? I am not sure. I'm willing to entertain suggestions. You can email me at
hawkowl@yahoo.com.
If you'd like to create your own maps from CBC data, you can go to Cornell Laboratory's
Birdsource website. Select "Christmas Bird Count". On the retrieved page, click on "Historical Data".
