I wasn't engaged in the online discussion last night. But looking at photos
this morning, the Dillon Reservoir loon has good potential to be an Arctic
Loon, which of course would be extraordinary anywhere in the eastern half
of North America.

It's a challenge to separate Arctic and Pacific loons in any plumage.
Typical individuals look distinctly different, but there is variation in
both species. There is variation (and some overlap) in all of the
characteristics that separate them, so there isn't any one simple yes/no,
on/off distinction that would be diagnostic by itself. Here we have to
build up a case with as many characteristics as possible, especially for a
bird so far outside its normal range.

This morning the bird in question was seen by a number of people, and then
it was seen to fly away. Still trying to find out whether anyone got photos
of the bird in flight. A good, clear photo of the underparts would be
helpful in pinning down the ID, but it would also be helpful to have as
many photos as possible of the bird on the water, showing things like head
shape, bill shape, nape color, pattern of the neck stripes, flank pattern,
and so on. A photo with the bird in direct size comparison to a Common Loon
would be a bonus. I suspect that the Ohio Bird Records Committee will want
to collect materials like this and send them to someone who has really
studied loon ID, such as Lars Jonsson.

If the bird is indeed an Arctic Loon, the big question would be which
source population it represents. The most likely would be the Siberian
subspecies, G. a. viridigularis, which nests in n.w. Alaska in very small
numbers (and may sometimes interbreed with Pacific Loon, producing
intermediates, which certainly makes the ID challenge more interesting).
But we can't dismiss the (remote) possibility of a transatlantic vagrant of
G. a. arctica coming across from Europe. I wouldn't expect that bird to
show up on a reservoir in Ohio, but birds do strange things.

At any rate, here's hoping that the bird will be refound so that it can be
enjoyed by more birders, and here's hoping that it can be pinned down to a
positive identification.

Kenn Kaufman
Oak Harbor, OH

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