Yellow-billed Loon (Gavia adamsii)
Pescadero Creek Mouth, San Mateo County, California
20 November 2006
Joseph Morlan

Photos © 20 November 2006 by Joseph Morlan. All rights reserved. Click here for full sized image.
Today, after learning that the Yellow-billed loon was still present at the Highway one bridge over Pescadero Creek, I decided to try for the bird. I arrived mid afternoon and several birders including Maryanne Danielson, Jean Marie Spoelman and Gary Strachan were in the parking lot with spotting scopes trained on the bird. Eventually the bird moved into the estuary on the west side of the bridge affording excellent views. It then moved under the bridge and upstream around the bend where it was not visible. I decided to walk out to the bend where I found the bird preening and dozing. Eventually George Griffeth arrived and I was able to show him the bird. It then swam back toward the bridge where I met Linda Swanson and several other birders. We all enjoyed the bird at close range. Gary Deghi arrived later as the bird was heading back upstream.


It was a large loon, similar to Common Loon (G. immer) but with a warmer brown coloration especially about the head. The bill was a pale ivory-yellow color all over including the culmen. This feature was particularly evident when we viewed the bird from above in the parking lot which overlooks the estuary. The face was rather blended with warm brown fading gradually to whitish around the eye and throat. A dark-brown slash was evident across the auriculars. The small eye appeared reddish. The head was rather blocky, but no more so than on a typical Common Loon. The side of the neck had a darker brown collar that blended with paler brown across the front of the neck. This pattern was more evident than on any Yellow-billed Loon I have seen before. The chest, breast and belly were white. The upperparts were brownish-bray with a scaly appearance. Each feather and a light buff scallop on the corner, but the fringe was broken by a dark tip along the shaft. The sides of the breast was mottled light gray and darker brown. The feet were set well back and appeared dark when the bird preened and rolled on its side. The underwings were quite pale in the wing coverts, but the side of the body under the spread wing was mottled with dark brown separating the wing coverts from the white belly. Photos show the maxillary feathering to extend to the distal end of the nostril.


The key feature which confirms this bird as a Yellow-billed Loon, is the all pale culmen. That of Common Loon is dark. Other supportive features include the blended face and neck pattern, the warm brownish overall coloration, very thick neck and the bill held at an upward angle.

This is a juvenile bird showing the strongly marked scapulars and mantle of that plumage. Adults in winter have a darker back with less contrasting fringes.

This bird was first tentatively reported as a possible Yellow-billed Loon by Frances Toldi on Saturday, November 18. This report was checked out the next day by Ron Thorn and Dan Singer who confirmed the identification. Today, when I arrived I learned from Sue James that she had seen the same bird on Tuesday, November 14 while scouting for a field trip for Santa Clara Audubon. She had never seen a Yellow-billed Loon before and assumed this bird was a Common Loon. However, the next day, during the field trip, a birder from Sweden identified it as a Yellow-billed Loon but did not offer reasons for that identification so she left it as a Common Loon. Sue said that she is sure that the bird she and her group saw was this bird. During the several hours I spent with the bird, we saw no other loons in the area and I believe the bird was very likely present since November 14.

Click here for video taken 19 November 2006 by Leslie Lieurance. Click here for an image taken this morning by Calvin Lou.