Just another "small picture" anecdotal observation which seems to
supplement the "big picture" postings:

Since I began observing in the woodlot and adjacent floodplain behind the
southwestern BC campus where I work, I regularly saw and heard OSFL every
summer from 1992 through 1995, often high in forest-edge western red cedars
overlooking the floodplain. For the summer of 1996 I had no OSFL at all.

Stan Olson
Abbotsford, BC
olson at twu.ca