A few thoughts I don't believe have yet been expressed concerning
cuckoos in WA and BC (sorry if I overlooked your comments):

1. The western race of the yellow-billed cuckoo appears to have more
selective habitat requirements than the eastern race. We may call
birds overshoots because they occur hundreds of miles north of other
birds. However, this distance may be more of a function of the lack of
suitable habitat rather than birds on steroids.

2. Cuckoos are one of the last birds to arrive in suitable habitat in
central California, often well into June. For years they may have been
overlooked in some areas because the birders (I among them)
quit looking in the riparian habitats after the "last" of the spring
migrants passed through in mid-May or so.

3. Many of the recent records could just as easily be overshoots from
the eastern populations. Given the low numbers of western birds and
a not insignificant rate of vagrancy of the eastern birds, I would
expect many of the recent records to be such.

--Jerry Tangren <tangren at wsu.edu>