Tweeters and Vancouver Birders,

To add some perspective to the recent discussion of Swainson's
Thrush arrival dates on TWEETERS, here is a list of arrival dates of
record for the Vancouver, B.C. area from 1968 through 1995:

1968 May 11
1969 May 10
1970 May 2
1971 May 2
1972 April 28
1973 May 20
1974 May 15
1975 May 14
1976 to 1979 no data
1980 May 11
1981 April 16
1982 May 8
1983 May 14
1984 May 15
1985 May 12
1986 May 17
1987 April 28
1988 May 10
1989 April 21
1990 April 28
1991 May 16
1992 April 16
1993 May 5
1994 May 10
1995 April 23


Average arrival date: May 6
Earliest arrival date: April 16 (1981 and 1992)

Note that the "first arrival" dates are in the second half of
April in 7 of the 24 years between 1969 and 1995. All these sightings
have been carefully screened, most are by experienced observers, and I
am confident that all, or nearly all, of them are based on correct
identifications.

At Vancouver, Swainson's Thrush arrives in numbers most years
around or shortly after May 10th. However, in some years at least,
there appear to be a few "early birds" which arrive up to 3 weeks
ahead of the main mass of migrants. I agree with Mike Patterson that,
for Swainson's Thrush, arrival dates should be based on birds seen,
not birds heard. Even then, identification should be made carefully,
because a briefly-glimpsed Hermit Thrush could be mistaken for a
Swainson's. It should be kept in mind that, even in the last week of
April and first week of May, Hermit Thrushes are far more numerous
than Swainson's anywhere in the Northwest.

An odd feature of both Swainson's and Hermit Thrushes is that they
normally do not sing when on migration. Swainson's, at least, normally
does not start singing until a good 10 days after it has arrived on
territory (May 20th or later in southwestern B.C.). This makes Vicki
Biltz' report of a singing Swainson's in April even more unusual than
it might seem otherwise.

I am a little surprised that Russell Rogers has only 6 April
records of Swainson's in WA (that's from 1993 onward, right?), and
that Mike Patterson has no records for his Astoria banding station
earlier than May 10th. I can only say that the Vancouver migration
data are summarized from the reports of dozens of active and
experienced observers in a heavily-birded area, and arrival dates
average perhaps a week or more earlier than you would get from the
records of any single observer. (It still doesn't explain why there
are so few April records for WA).

Conclusion: Swainson's Thrushes may not be quite as unusual in late
April as suggested by Rogers and Patterson, but are still very scarce
in April, with large numbers not arriving until May 10 or later.
Swainson's Thrushes in April should be carefully documented, and care
should be taken to avoid confusion with Hermit Thrushes.

Wayne C. Weber
Kamloops and Delta, B.C.
wayne_weber at bc.sympatico.ca