My gut feeling "on the ground" (having done a couple of contracts in woodlands in the hills of N Wales), is that they are declining/shrinking in range, particularly woods on the fringes of their ranges. One wood where I've had them previously - Coed Dinorwic, Llanberis - we surveyed 4 times between mid April and late June, and didn't get a single Wood Warbler. It would be tempting to assume that any increase in Argyll corresponds to the decline in SE Britain. I should say, I haven't done any statistical analysis on the data I've generated.
Redwoods speak to me,
say it plain:
"the Human name
doesn't mean shit to a tree." Jefferson Airplane, Eskimo Blue Day.