Do you often find that threads about squirrels affect your quoting skills, too? 
I haven’t tried PBR, but I’ve found them sniffing-around the empty Negra Modelo bottles before.
I wonder if they go after the same spot repeatedly because it’s easy to access? The boards look pretty closely spaced in the photo, so many the fact that it’s already been chewed on makes it easier to get a mouthfill, versus trying to nibble on the flat top of another board. If that board had an imperfection to begin with such as a large splinter or larger than average gap between that and another plank, it could be why that one was chosen over others. I have no idea why they would go for one spot on a roof, though- seems like all the shingles would provide equal edge-area for them.