Greetings Again

I read some swallow discussion on OBOL and arranged my thoughts on the
swallow incursion more carefully. See below

The swallow phenomenon is most interesting. It is important to note that
these can occur at any time during winter, that the birds are virtually never
stationary (ie, they almost never linger at one location), and that Barn
Swallows predominate. It is also important to note that Barn Swallows are
considered casual to very rare during winter even in Santa Barbara and Orange
Counties in southern California.

Given the above, I think we can be pretty certain about the following:

1) With the possible exception of some early December birds, the winter Barn
Swallows are not lingering fall or early spring migrants, in the sense of a
daylength inspired latitudinal movement.

2) These birds are not overwintering.

That does not leave many options. The leading contender is that these birds
are moving north on persistent southerly winds. These conditions are not rare
in the Pac NW and are often associated with heavy rainfall. To PROVE the
wind/swallow relationship, a careful analysis of this year, and past years,
would be necessary.

More interesting, and less answerable, is WHY. Unlike bluebirds and robins
that sometimes wander north as the weather warms, Barn Swallows are in a much
more precarious position. They are not frugivores to any significant extent
(Tree Swallows, and I believe, VG Swallows can survive on fruit for periods
of time - hence their tendency to winter further north and arrive much
earlier in the spring). When a Barn Swallow wanders a thousand miles north of
its normal winter range, it is in a very tenuous position. It is hard to
imagine that these birds are not doomed. Furthermore, why are these northward
movements mostly Barn Swallows. Why not the more northerly wintering
Tree/VGs? Why not Cliff Swallows, which share a similar winter range?

Interestingly, Common Swifts nesting in northern Europe, are known to leave
their nest sites for days or more following the leading edge of low pressure
systems, returning to their nest sites after the storm has left. The young
are adapted to these long absences, and if the adults remained during the
storm, they would be unable to feed. This escape movement allows the adults
to continue feeding while the storm passes. I don't think that the winter
Barn Swallow incursions are analogous, however, and I can't see an advantage
for a midwinter visit to the dangerous (for a swallow) northwest. It would be
most interesting to know where they are coming from and if any survive to
return south.

Cheers
Steven Mlodinow
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