Black walnut phenology

I wish I knew

why the black walnut trees in our yard still have lots of leaves, even though it’s October already! The ones lining the county road less than half a mile away away lost their leaves long ago, as self-respecting Juglans nigra should. The photo above is of some that had mostly lost their leaves by September 20, which is still a bit late in the year to have as many as are shown. But those in our yard still have lots more than that.