This is a progress report. We haven't yet solved the squirrel-in-the-owl-box-problem. But I believe we are getting closer.
The squirrels aren't early birds. Usually I hear the alarm between 9:00 and 10:00 AM and dash to the window to see what's going on. By then the squirrel is in the owl box. The regulars seem to be young of last year, perhaps siblings.
Since my last report they visited and fed in the open-topped box for a week. Then I put the roof back on, and they had to get past the overhang of 2.5".
As expected, there was no contest. They just hang over the front and enter.
After a week of regular morning visits I extended the length of the overhand from 2.5" to 6.75". Again, they didn't miss a beat. Their rotational ankles make it easy to cling to the front edge of the box and reach the entrance.
This afternoon I extended the roof to 9". The squirrels will have to span 11" to reach the hole from the front edge of the roof.
I expect they'll start coming in from the side, where the straight line distance to the hole is 6.75".
I just hope they don't lose their appetite for sunflower seeds, so we can finish the trials in the next two weeks.
Oh yes, something else is going on, too. Yesterday's squirrel had a bloody patch of skin on one side of its face, and this morning another squirrel showed up with a bloody snout. Has mom become a pre-partum crankinpuss, and is she kicking butt when last year's litter shows up in the nest? I wonder.