Date: 1/7/18 7:44 pm From: David Irons <LLSDIRONS...> Subject: [obol] Swan ID: Some comments about a group of seven Trumpeter Swans that appear to be wintering at Coffenbury Lake in Fort Stevens State Park (Clatsop Co)
While birding around Brownsmead this morning, Shawneen and I ran into Mike Patterson, who as always provided a wealth of information about local birds of interest. He told us about a group of seven Trumpeter Swans that have been at Coffenbury Lake (in Fort Stevens State Park) for a few weeks. As Trumpeter Swan would be a county bird for both of us, we decided to check them out in the midst of our fruitless (and quite wet) search for White-winged Crossbills this afternoon.
We had lengthy yet somewhat distant scope views of the swans from parking lot at the south end of Coffenbury Lake, with the birds about halfway up the lake. In looking at the adult birds, both Shawneen and I were struck by how "pinched" the facial skin was right in front of the eye. I have always looked for a more evenly tapered wedge of black facial skin meeting and to some degree enveloping the eye. Although distant, these adult birds did not seem to have this expected look. After studying the swans the best we could, Shawneen pulled up a number of recent reports of these birds on eBird. Many of them include excellent photos of both the adult and immature birds. These photos paint a slightly ambiguous picture, with the facial skin looking very pinched and Tundra-like in some of the photos and broader and more wedge-shaped (a Trumpeter characteristic) in others. There is at least one photo that shows the white feathering in the center of the forehead meeting in a decided point–another good mark for Trumpeter. Finally, in all of the photos the upper ridge of the bills of these birds is very straight with no concavity–again good for Trumpeter. It should be noted that the young birds are darker than one would expect for immature Tundras, another mark favoring Trumpeter.
After some initial confusion and extensive review of photos of these birds and other Trumpeter and Tundra Swan photos online, we have comfortably concluded that they are Trumpeters. I have perhaps been overvaluing the shape of the facial skin where it meets the ID when sorting out Tundra and Trumpeter Swans. Changes in photo angle no doubt affect how straight or convex the line of demarcation is where the white feathering meets the skin at the base of the bill.