This may or may not be helpful, from PRBO's species account (yes, I know -- Pt. Blue).
Departure date from breeding grounds: According to McCaskie (1988),
departs Coast and Mountain regions late August through October. PRBO banding
data for Marin County (1996 and 1997) -- latest capture dates October 16, 1996
and October 4, 1997.
Spring and Fall migration period: While SWTH is rare in Interior and
Basin regions during the summer months, abundance peaks in Spring (April through
May) and Fall (August through September) in these regions (McCaskie 1988) --
possibly indicating peak of Spring and Fall migration period in California.
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And at the same time, we're on the front end of Hermit Thrush arrival dates.
