bird counts

It's quite possible that what you say is true. I always repeat the walk at this time of year-very late April or very early May, to keep continuity. And I've been doing my tetrad visits in May and June for partly for the reasons you've stated and obviously partly because some species haven't arrived at all yet. I suppose the best way to check would be to repeat the visit on one or more occasions later in the season. Perhaps the reduced numbers tell us that fewer Willow Warblers are passing through Cross Inn Forest?Anyway, I think I'm rambling on a bit. Too much to think about. Too little time!