Date: 1/8/25 7:11 pm From: 'Glen Tepke' via mbbirds <mbbirds...> Subject: Re: [MBBIRDS] possible Arctic Loon (belated report)
As Emily Litella would say, Never mind! (To those who got that dated
cultural reference, don't forget to renew your AARP membership.)
I have been advised by the authorities that the loon is neither Arctic
nor Pacific, but is actually a Red-throated Loon. I had considered
RTLO, but thought that species would show a straighter, less curved
culmen (top edge of the bill), more white around the eyes and side of
the neck, less white at the top of the flanks, and lighter gray plumage
in the back and wings. We saw another RTLO on the count that fit that
description, and the bird in question looked quite different to me, but
apparently it is within the range of variation for all of those
characteristics, and the white spotting on the back and wings is more
consistent with RTLO. Oh well, live and learn. Thanks to Alex Rinkert,
Brian Sullivan and Don Roberson for the educational experience.
Good birding,
Glen Tepke
On 1/8/2025 1:39 PM, 'Glen Tepke' via mbbirds wrote:
> 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.
>
> Looking forward to your comments.
>
> Good birding,
>
> Glen Tepke
> Santa Cruz
>
>
>
>
>
