I am taking the liberty of copying below a post from Bill Maynard regarding a supposed Arctic Loon in Franktown, Colorado. It gives ID specifics.
There are few records of Arctic Loon south of Alaska. If it really is an Arctic Loon, it may be the first interior U.S. record. Neverthless, we've had Smews and Red-necked Stints and other crazy Eurasian birds around here. We might as well start looking carefully at "Pacific" Loons. Who knows, maybe an Arctic will turn up  if we start looking for it.
By the way, the key initial field mark for Arctic is a white flank patch. If you don't see that, don't worry. If you do see it, take careful notes. The other field marks are tricky.
Bob Fisher
Independence, Missouri
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There were approximately 20 birders at the Franktown, Walker Road Pond
viewing the loon this morning.  I would recommend reading the April 1997
issue of Birding by Cin-Ty Lee for specific information including photos and
drawings on separation of Arctic from Pacific Loons.  Those of us who
watched the bird for a few hours saw the following features that make it an
Arctic Loon.

Age: The loon has retained some of its adult breeding plumage and is molting
into adult basic.

The bird shows a block head and long bill of an Arctic Loon vs. the round
head and delicate bill of a Pacific Loon.  If you watch the loon after it
has been diving a lot, the head looses some of its blockiness and can appear
a bit round. The bill is often angled up similar to what you would look for
in a Red-throated Loon, a characteristic of Arctic Loon.

Although there is at times a suggestion of a chin-strap which a Pacific Loon
in basic plumage has, this feature appears to really be the result of dusky
feathers that remain from the alternate plumage.  If you can get a good look
at the bird when it is swimming face on, the chinstrap look disappears. The
chinstrap feature is not a definitive method of separating the 2 species but
is suggestive using the other characters.

Pacific Loons have a dark band across their vents called a vent strap.
Early this morning the loon rolled over on its side and there appeared to be
a band from a distance which I believe was actually one of its legs hanging
down.  However, as the loon swam closer to us and rolled at least three
additional times, it was apparent that the undersides were immaculate,
without a vent band. This has been documented in a clear digital photograph.

Flank color is the most obvious field mark to look for.  This loon has
obvious white flanks on both sides and sometimes shows extensive white while
it is loafing.  When it is actively diving the white flanks often show only
on the hind parts, a feature which is consistent with Arctic Loon.

Rarity:  There are few if any inland records for Arctic Loon. The Franktown
bird has been quite accommodating and has provided very good scope views.
Urling and Hugh Kingery first found the bird Sunday and reported noticing
it's white sides.  Glen Walbeck went Monday and took some very convincing
photos.  Today, the rest of us took advantage of their work.

Bill Maynard
Monument Colorado
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