Hi Tweets,

Regarding a possible Pacific (PALO)/Arctic Loon (ARLO) ID, Don Cecile writes:

>... but it had white sides! Taken
>by itself, this field mark is rather useless but is very visible from a long
>distance and would likely be the first field mark that would steer an
>observer into speculation.

Yes, indeed!

> It was in
>basic plumage, a few white spots were appearing on the otherwise dark
>mantle. I thought it's profile was smooth and sleek like a Pacific Loon, it
>should be more block-headed for Arctic, approaching the head-shape of Common
>Loon.

Open to question, as apparently bill size in the Siberian race of ARLO Gavia
arctica viridigularis shows variation from same size as that of PALO G.
pacifica to perceptibly larger in the field, but is typically larger, and
typically larger than the nominate race to the west. As far as its profile
as a basic-plumaged bird goes, wasn't aware of any difference.

>The white sides appeared to darken toward the rear flanks and I
>thought this area should still be rather white for an Artic Loon.

This suggests PALO: most of the photographs I've seen of ARLO show that the
white looks like a horizontal white bar that expands into a wider white
flare or comma on the rear flank. My count-partner that year, Karen Wiebe,
and I did have a close sighting of one ARLO off the Roberts Bank Coalport
Jetty in Ladner BC on a Ladner Christmas Count. It showed the white
bar-and-flare combination *very* conspicuously (and a larger than normal
bill for PALO). Sidebar: Though it had all the features of ARLO and the
observation and ID was *very* cautiously and provisionally endorsed by Terry
Walsh, who had just published an article in Birding on the separation of
PALO & ARLO, (and who said in his comments on the Ladner sighting that our
description included an ARLO feature he hadn't even mentioned in his
article), the local committee rejected it on grounds that even today seem
quite unclear, and had little to do with the sighting itself; there seems to
be no written recognition of the sighting anywhere I've looked, either,
though we reported it to the Count organisers and submitted a description
when we were sure of the ID. After this sort of treatment, I've never done
another Ladner CBC, no matter how tasty some of the birding is. Well, that's
the way we do things in BC. Oh boy, don't get me started.

>No
>chinstrap was visible but the bird was much too far away to see this.
>The bill was held horizontally as one would expect for Pacific Loon.

I think both typically do this. The Ladner bird did.

>1) What would be the most likely time to find an overdue Arctic Loon in the
>Pacific Northwest?

No one knows. I'd guess it likely for one to fall in with a southbound crowd
of PALO. Start looking at clusters of arrival and departure dates of both to
know when to start looking in earnest; try to suss out where their wintering
destinations are or might be. For a start, PALO average arrival & departure
dates for Vancouver BC are 9/09 and 5/11 repectively. Any migrant bird
follows a schedule; we just have to figure it out. The Ladner CBC bird was
Week 1 January 1987. I remember Al Jaramillo mentioning that Asian strays
would likely follow the same latitudinal timing down either coast. So, maybe
find out from Birds of the Western Palearctic when ARLO in the Bering Sea
start moving S and start looking among migrant PALO here in and after that
period. Once we become more confident of field-mark differences, our
observations may (and I'd guess will) show they're a regular rarity on the
order of Yellow-billed Loon. For sure, though, there's at least a decade or
two's worth of work to do to find out what the ARLO migrational and
wintering patterns on the West Coast are, as well as their observable numbers.

>2) would one expect to find an arctic loon in a mixed flock with Pacifics?
>or by itself?

This bird wasn't far away from Point Roberts WA, where quite few winter and
stage through in either direction. I'd guess an ARLO would be with a PALO
flock: the PALO would have found where the food would be.

>3) what are the chances of finding one close enough to shore that one might
>be better able to scrutinize its markings rather than relying on potentially
>misleading field marks like the bird in question. ( in other words, do
>Arctics prefer deeper waters?)

The Ladner bird was an adult in Definitive Basic plumage, close in,
sometimes no more than 20 meters (60 ft) from shore on oily calm water for
fifteen minutes at the far end of the jetty; whether this is typical I don't
know. A bird might not think being close to a jetty as being close to shore.
At the point of observation, there was a high tide over sandflats, so the
water wasn't much more than four or five meters deep. It was pretty dozy,
catnapping on the surface.

One thing is clear at this point, Don, and that your approach is absolutely
the proper one: not relying on one field-mark alone, no matter how
suggestive or conspicuous.

Michael Price
Vancouver BC Canada
mprice at mindlink.net