Date: 1/8/25 1:40 pm From: 'Glen Tepke' via mbbirds <mbbirds...> Subject: [MBBIRDS] possible Arctic Loon (belated report)
On New Year's Day I participated in the "pelagic" section of the Moss
Landing Christmas Bird Count, which covers a slender crescent of inshore
Monterey Bay from La Selva Beach to Moss Landing. At 9:58 a.m. I
photographed a loon as it flew in front of the boat roughly a mile west
of Moss Landing in Monterey Co. waters. My first impression, based
solely on size, was a Common Loon, but when I noticed the
moderately-sized dagger-shaped bill and the fairly clean straight border
between black and white on the neck, I recorded it as a Pacific Loon and
gave it no more thought. I've been pretty busy since then, including
doing two more CBCs, and didn't get around to looking at the photos
until last night.
After studying the Sibley, Nat Geo and Harrison, Perrow & Larsson
Seabirds field guides, the species accounts in Birds of the World, and
hundreds of photos in the Macaulay Library, several features of the bird
have me wondering if it could be an Arctic Loon (in definitive basic
plumage per the plumage descriptions in Birds of the World):
- The white on the flanks wraps up toward the rump, with the highest
white above the base of the wings. I did not see the bird sitting on
the water, but the white appears to be high enough for a white patch to
appear above the waterline if it was sitting, which is the key field
mark for separating Arctic from Pacific. I looked at many flight shots
of both species in the Macaulay Library and didn't see any Pacific Loons
with white wrapping that high.
- No dark chin strap. Most, but not all, Pacific Loons have a thin dark
stripe running around the throat. My sources provide conflicting
information on how often Arctic Loon shows a chinstrap, but the
consensus seems to be that it is less often than in Pacific.
- No dark vent strap. Most Pacific Loons have a dark stripe running
between the bases of the legs; in Arctic Loon the vent strap is often
incomplete or absent.
- Dark gray nape and hindneck, just a little lighter the rest of the
upperparts. Pacific Loon usually has a contrasting lighter gray nape
and hindneck.
- Clean white cheeks. Pacific Loons generally have duskier cheeks, but
the difference can be subtle.
- Arctic Loon is generally larger than Pacific, but there is overlap.
As I mentioned above, my impression was of a large loon, but that is
very subjective and there were no other loons present for comparison, so
I am not putting any weight on size.
On the other hand:
- This bird does not show the steeper forehead and slightly peaked crown
of Arctic compared to the more rounded head of Pacific, but that feature
seems to be more noticeable on birds sitting on the water than on birds
in flight.
- Arctic Loon generally has a longer and stouter bill than Pacific, but
the bill on this bird seems to be within the range of variation for both
species.
Three of the best photos are in this checklist -
https://ebird.org/checklist/S207504339 - under Arctic/Pacific Loon. I
have several more photos, but I don't think they show anything different.
Note that we also saw what I think is an adult Glaucous Gull in the same
area, but my photos are horribly out of focus, so best not to look at those.
