Alvaro Jaramillo wrote:

> Dave DeSante also believes that coastal California American
Robins> nest here early in the season then move up to the Sierras to
breed> a second time, he has some banding info to support this, but
not
> enough to convince anyone yet.

This is suspected for a few species in Europe as well.

Early each June in Scotland there is a fresh arrival of male
whitethroats (Sylvia communis) which take up territories and start
singing. I suspect these are birds from further south which may have
failed breeding and are trying their luck further north where the
Spring is just getting going. Proving this however will take some
doing as the numbers of whitethroats banded each year in the UK is
almost vanishingly small.

A similar situation exists with dotterel (Charadrius morinellus). A
male was banded while sitting on a clutch of 4 eggs at Drumochter
Pass, Scotland in late May. Six weeks later the bird was seen on the
Hardangervidda in southern Norway with a brood of chicks.
Presumably the bird failed in Scotland and moved further north to
try again (it's a bit far to walk and the North Sea gets in the
way). There are also a couple of records of (color-banded) female
dotterel seen on Scottish mountains displaying then seen a few weeks
later in southern Norway.

Whether birds in the UK migrate between broods is open to question.
I suspect not, given that the weather conditions are relatively
benign, with no summer "drought" typically associated with large
areas of the US.

Still I think it's a matter of time before this "opportunistic
migration" is demonstrated as a real breeding strategy. The only
thing hampering its demonstration is a lack of banders ;-)

See ya,

Stuart
---
Stuart MacKay
220-301 Calibre Chase Drive
Raleigh, NC 27609
ph:(919) 832 0353
email: stuart at blarg.net