Andy wrote -

<much re. Steller's Eider deleted>

>By the way, whats going on in the arctic this fall to send our way more
>than usual #'s of Red Knots, Long-tailed Jaegers, Sabine's Gulls and now...a
>Steller's Eider? Any connection to all this?

I was at work at the P.G. weather office when I read your note, Andy,
and it tweaked my curiosity since I have been wondering the same
thing. A few questions have to be pondered before we can begin. What
is the:

1) source region of species;
2) usual migration chronology, route and destination;
3) incidence of vagrancy.

Let's assume that these are all birds of Alaskan origin, made more
plausible by the Steller's Eider showing up. Most of these birds begin
migration around the same time, although the eider likely starts
later. The gull and jaeger are headed for the austral sunshine usually
via an offshore route; the knot to Californian or Mexican shores via
the coastlines; while the Steller's does a short hop across the Bering
Sea to the Aleutians for the winter. The only really totally
out-of-range bird is the eider with only a few records at these
latitudes. But the eider, and to a lesser extent the gull, are the
keys here, I think, since their presence suggests an eastward or
southeastward displacement to the usual migration pattern.

The next leap of faith is needed when trying to determine causal
factor. Just to take the obvious, let's assume it was the weather.
Have there been any weather patterns the past month or so which could
have produced such a displacement? As it happens, yes, there have
been. The Arctic enjoyed a relatively balmy breeding season again this
year while we were suffering our cold low fever. However, the boreal
summer came to a crashing end with the premature establishment of the
polar vortex around the middle of the month. An attendant early season
Arctic front began to descend on the north slope, pushing down to
about 65N latitude by the third week. One assumes that this defines
the end of the window for the beginning of the southward migration.
Fine, so this provides a southward impetus. Why were they displaced to
the east?

The weather pattern across North America most of the summer consisted
of upper troughs off both coasts and a big, hot ridge up the middle of
the continent. Another flatter ridge extended south from western
Alaska, while the strongest, hottest ridge since 1976 lay along the
European coast. During most of July, but especially in August, a
parade of low pressure systems rode up along the Aleutians atop the
offshore ridge then plunged into the base of the trough just off the
coast where they became our well-known cold lows which then meandered
onshore and made our lives miserable. If one pictures these storms as
giant vacuum cleaners (not a bad analogy, really), then it is easy to
see how birds could be "sucked up" in this storm track along the
Aleutians, taken for a ride into the Gulf of Alaska, and then
"escaping" as the storm wound down into a cold low. Given the
counterclockwise rotation around northern hemisphere lows, the winds
would have pushed these birds toward the coast.

The whole pattern began a wavelength change near the end of August,
and by the first week of September had completely reversed itself with
the establishment of a big ridge along the west coast and cold troughs
over eastern N.A. and another south from western Alaska. The remnants
of the last cold low of this six-week series are just now fading away
in Montana (get ready for a big warmup in Washington!). The current
storm track is still along the Aleutians but splits near Prince
William Sound with the majority barreling eastward along 60N and
another part plunging southward into a new cold low formed well
offshore of northern California.

So, we have Arctic air as the impetus for the southward movement; and
an active storm track travelling the length of the Aleutians into the
Gulf of Alaska as a probable reason for an eastward displacement. A
squeeze from the north and a push from the west. Of course, weather is
only one plausible factor, but given the number of affected species
and its broad-scale manifestations, it seems the most likely to me.

- Jack