This fresh carcass on the south shore of Long Island was in perfect condition, apparently the result of a gunshot. It weighed quite a bit (8 lbs??), which rules out the smallest loon species, Red-throated and Pacific Loons, and favors Common Loon over Arctic. The bill is on the small end for Common Loon, and possibly at the largest extreme for Arctic Loon. The black-mottled throat suggests Arctic Loon (Gavia arctica). Harrison (Seabirds , an Identification Guide, revised edition 1985) describes the basic adult Gavia arctica ("Black-throated Diver") as sometimes having mottled throat, and spotting on wing coverts. The white eye-arc is a Common Loon feature. Comments?
Comment received from Tom Magarian (biologist at Cape May Bird Observatory): "This is most definitely a common loon by plumage. The white spotting goes all the way across the top of the back. Pacific/arctic would have spotting more on the sides of the back, with the center/top of back being mostly black. The white spotting on the wing coverts would be much larger in pacific/arctic as well."
Other comments received through NYS-L and BirdForum generally support the identification of this loon as a Common Loon, although Arctic also received some votes. Thanks to all who provided input on this loon's identity.
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